Growth plasticity of the embryonic and fetal heart

The developing mammalian heart responds to a variety of conditions, including changes in nutrient availability, blood oxygenation, hemodynamics, or tissue homeostasis, with impressive growth plasticity. This ensures the formation of a functional and normal sized organ by birth. During embryonic and fetal development the heart is exposed to various physiological and potentially pathological changes in the intrauterine environment which dramatically impact on normal cardiac function, tissue composition, and morphology. This paper summarizes the mechanisms employed by the embryonic and fetal heart to adapt to various intrauterine challenges to prevent or minimize postnatal consequences of impaired cardiac development. Future investigations of this growth plasticity might lead to new therapeutic strategies for the prevention of cardiac disease in postnatal life.     

Regenerating cardiac cells: insights from the bench and the clinic

A major challenge in cardiovascular regenerative medicine is the development of novel therapeutic strategies to restore the function of cardiac muscle in the failing heart. The heart has historically been regarded as a terminally differentiated organ that does not have the potential to regenerate. This concept has been updated by the discovery of cardiac stem and progenitor cells that reside in the adult mammalian heart. Whereas diverse types of adult cardiac stem or progenitor cells have been described, we still do not know whether these cells share a common origin. A better understanding of the physiology of cardiac stem and progenitor cells should advance the successful use of regenerative medicine as a viable therapy for heart disease. In this review, we summarize current knowledge of the various adult cardiac stem and progenitor cell types that have been discovered. We also review clinical trials presently being undertaken with adult stem cells to repair the injured myocardium in patients with coronary artery disease.     

Cardiac endocrine function is an essential component of the homeostatic regulation network: physiological and clinical implications

The discovery of cardiac natriuretic hormones required a profound revision of the concept of heart function. The heart should no longer be considered only as a pump but rather as a multifunctional and interactive organ that is part of a complex network and active component of the integrated systems of the body. In this review, we first consider the cross-talk between endocrine and contractile function of the heart. Then, based on the existing literature, we propose the hypothesis that cardiac endocrine function is an essential component of the integrated systems of the body and thus plays a pivotal role in fluid, electrolyte, and hemodynamic homeostasis. We highlight those studies indicating how alterations in cardiac endocrine function can better explain the pathophysiology of cardiovascular diseases and, in particular of heart failure, in which several target organs develop a resistance to the biological action of cardiac natriuretic peptides. Finally, we emphasize the concept that a complete knowledge of the cardiac endocrine function and of its relation with other neurohormonal regulatory systems of the body is crucial to correctly interpret changes in circulating natriuretic hormones, especially the brain natriuretic peptide.     

Exogenous ketone ester administration attenuates systemic inflammation and reduces organ damage in a lipopolysaccharide model of sepsis

AimsSepsis is a life-threatening condition of organ dysfunction caused by dysregulated inflammation which predisposes patients to developing cardiovascular disease. The ketone β-hydroxybutyrate is reported to be cardioprotective in cardiovascular disease and this may be due to their signaling properties that contribute to reducing inflammation. While exogenous ketone esters (KE) increase blood ketone levels, it remains unknown whether KEs can reduce the enhanced inflammatory response and multi-organ dysfunction that is observed in sepsis. Thus, this study assesses whether a recently developed and clinically safe KE can effectively improve the inflammatory response and organ dysfunction in sepsis.Methods and resultsTo assess the anti-inflammatory effects of a KE, we utilized a model of lipopolysaccharide (LPS)-induced sepsis in which an enhanced inflammatory response results in multi-organ dysfunction. Oral administration of KE for three days prior to LPS-injection significantly protected mice against the profound systemic inflammation compared to their vehicle-treated counterparts. In assessing organ dysfunction, KE protected mice from sepsis-induced cardiac dysfunction as well as renal dysfunction and fibrosis. Furthermore, KE administration attenuated the sepsis-induced inflammation in the heart, kidney, and liver. Moreover, these protective effects occurred independent of changes to enzymes involved in ketone metabolism.ConclusionThese data show that the use of an exogenous KE attenuates the dysregulated systemic and organ inflammation as well as organ dysfunction in a model of severe inflammation. We postulate that this exogenous KE is an appealing and promising approach to capitalize on the protective anti-inflammatory effects of ketones in sepsis and/or other inflammatory responses.     

The effects of right ventricular apical pacing on left ventricular function. Stimulation of the right ventricular apex: should it still be the gold standard?

Current pacing practice is undergoing continuous and substantial changes. Initially pacing had an exclusively palliative role, since it was reserved for patients developing complete heart block or severe symptomatic bradycardia. With the appearance of novel pacing indications such as pacing for heart failure and atrial fibrillation, the effect of pacing site on cardiac function has become a critically important issue and a subject for consideration. It seems that the classical pacing site in the right ventricular apex is no longer the gold standard because of possible disadvantageous effects on cardiac function. The aim of this review article is to discuss the effect of right ventricular apical pacing on cardiac function including cellular and hemodynamic changes. We also aim to discuss the role of alternative pacing sites in the light of cardiac function.     

Physiological development of the embryonic and larval crayfish heart

The cardiovascular system is the first system to become functional in a developing animal and must perform key physiological functions even as it develops and grows. The ontogeny of cardiac physiology was studied throughout embryonic and larval developmental stages in the red swamp crayfish Procambarus clarkii using videomicroscopic dimensional analysis. The heart begins to contract by day 13 of development (at 25 degrees C, 20 kPa O(2)). Cardiac output is primarily regulated by changes in heart rate because stroke volume remains relatively constant throughout embryogenesis. Prior to eclosion, heart rate and cardiac output decreased significantly. Previous data suggest that the decrease in cardiac parameters prior to hatching may be due to an oxygen limitation to the embryo. Throughout development, metabolizing mass and embryonic oxygen consumption increased, while egg surface area remained constant. The surface area of the egg membrane is a constraint on gas exchange; this limitation, in combination with the increasing oxygen demand of the embryo, results in an inadequate diffusive supply of oxygen to developing tissues. To determine if the decrease in cardiac function was the result of an internal hypoxia experienced during late embryonic development, early and late-stage embryos were exposed to hyperoxic water (PO(2) = 40 kPa O(2)). Heart rate in late-stage embryos exposed to hyperoxic water increased significantly over control values, which suggests that the suppression in cardiac function observed in late-stage embryos is due to a limited oxygen supply.     

The heart and control of renal excretion: neural and endocrine mechanisms.

There has been a great deal of research concerning the heart being an important regulator of renal fluid and electrolyte excretion. This cardiac-renal connection involves two different types of major mechanisms, both of which are covered in this review. The first of these to be discovered was neural reflex regulation. This type of control is due to the fact that the heart possesses nerve receptors whose activity is altered by changes in the degree of cardiac stretch that occur as a result of changes in blood volume. These receptors affect various humoral, neural, and perhaps hemodynamic mechanisms that modify renal excretion. A second, more recently discovered type of regulation is based on the concept that the heart is also an endocrine gland. Similar to neural receptor activity, cardiac hormone secretion is also linked to the degree of cardiac stretch or filling. These cardiac peptides have been shown to have a variety of physiologic effects, most of which directly or indirectly affect renal excretion. Both of the above cardiorenal control mechanisms, one neural and one humoral, may be important not only in maintaining normal fluid-electrolyte balance but may also have pathophysiologic relevance.     

MicroRNAs in a hypertrophic heart: from foetal life to adulthood

The heart is the first organ to form and undergoes adaptive remodelling with age. Ventricular hypertrophy is one such adaptation, which allows the heart to cope with an increase in cardiac demand. This adaptation is necessary as part of natural growth from foetal life to adulthood. It may also occur in response to resistance in blood flow due to various insults on the heart and vessels that accumulate with age. The heart can only compensate to this increase in workload to a certain extent without losing its functional architecture, ultimately resulting in heart failure. Many genes have been implicated in cardiac hypertrophy, however none have been shown conclusively to be responsible for pathological cardiac hypertrophy. MicroRNAs offer an alternative mechanism for cellular regulation by altering gene expression. Since 1993 when the function of a non‐coding DNA sequence was first discovered in the model organism Caenorhabditis elegans, many microRNAs have been implicated in having a central role in numerous physiological and pathological cellular processes. The level of control these antisense oligonucleotides offer can often be exploited to manipulate the expression of target genes. Moreover, altered levels of microRNAs can serve as diagnostic biomarkers, with the prospect of diagnosing a disease process as early as during foetal life. Therefore, it is vital to ascertain and investigate the function of microRNAs that are involved in heart development and subsequent ventricular remodelling. Here we present an overview of the complicated network of microRNAs and their target genes that have previously been implicated in cardiogenesis and hypertrophy. It is interesting to note that microRNAs in both of these growth processes can be of possible remedial value to counter a similar disease pathophysiology.     

Heart development in Drosophila

The Drosophila heart, also called the dorsal vessel, is an organ for hemolymph circulation that resembles the vertebrate heart at its transient linear tube stage. Dorsal vessel morphogenesis shares several similarities with early events of vertebrate heart development and has proven to be an insightful system for the study of cardiogenesis due to its relatively simple structure and the productive use of Drosophila genetic approaches. In this review, we summarize published findings on Drosophila heart development in terms of the regulators and genetic pathways required for cardiac cell specification and differentiation, and organ formation and function. Emerging genome-based strategies should further facilitate the use of Drosophila as an advantageous system in which to identify previously unknown genes and regulatory networks essential for normal cardiac development and function.     

Beta-adrenergic receptors of the normal heart and in heart failure

The heart is often refereed to as an "beta-adrenergic organ" because beta-adrenergic agonists are powerful stimulants of cardiac contractility. Catecholamines acting through beta-adrenoceptors produce both positive inotropic and chronotropic effects in human heart. It is now generally accepted that in human heart both beta 1- and beta 2-adrenoceptors coexist. beta-Adrenergic transduction system consist of membrane-bound beta-receptors, the effector enzyme adenylyl cyclase and guanine nucleotide-binding transduction (G) proteins. Repeated long-lasting agonist stimulus evokes homologous or heterologous desensitization of transduction system. Chronic heart failure accompanies with decreased responsiveness to beta-adrenoceptor agonists and is thought to exacerbate the loss of cardiac contractility. Depending on the etiology of heart failure abnormalities of the beta-receptor-G protein-adenylyl cyclase system result from a reduced of beta 1-receptors, uncoupling of beta 1- or beta 2-receptors, alteration of G-protein function, or decreased catalytic subunit activity of adenylyl cyclase and enhanced expression of beta-adrenoceptor kinase. The model most widely used is that of circulating lymphocytes that contain a homogeneous population of beta 2-adrenoceptors. The biochemical and pharmacological properties of human lymphocyte beta 2-adrenoceptors are quite comparable to those of heart beta 2-receptors. The analysis of lymphocyte beta 2-adrenoceptor-adenylyl cyclase system can be used as a model for long-term regulation of human cardiac beta 1- and beta 2-adrenoceptors only if serial changes in response to administration of non-selective beta-adrenergic agonists or antagonists are being investigated. This review concentrates on beta-adrenoceptors in human healthy heart and in heart failure and also on lymphocyte beta 2-adrenoceptors and on the changes of these receptors properties under the influence of some cardiotropic drugs.     

Redox ratio in the left ventricle of the growth restricted fetus is positively correlated with cardiac output

Intrauterine growth restriction (IUGR) is a result of limited substrate supply to the developing fetus in utero, and can be caused by either placental, genetic or environmental factors. Babies born IUGR can have poor long-term health outcomes, including being at higher risk of developing cardiovascular disease. Limited substrate supply in the IUGR fetus not only changes the structure of the heart but may also affect metabolism and function of the developing heart. We have utilised two imaging modalities, two-photon microscopy and phase-contrast MRI (PC-MRI), to assess alterations in cardiac metabolism and function using a sheep model of IUGR. Two-photon imaging revealed that the left ventricle of IUGR fetuses (at 140–141 d GA) had a reduced optical redox ratio, suggesting a reliance on glycolysis for ATP production. Concurrently, the use of PC-MRI to measure foetal left ventricular cardiac output (LVCO) revealed a positive correlation between LVCO and redox ratio in IUGR, but not control fetuses. These data suggest that altered heart metabolism in IUGR fetuses is indicative of reduced cardiac output, which may contribute to poor cardiac outcomes in adulthood.     

Extracellular matrix, mechanotransduction and structural hierarchies in heart tissue engineering

The spatial and temporal scales of cardiac organogenesis and pathogenesis make engineering of artificial heart tissue a daunting challenge. The temporal scales range from nanosecond conformational changes responsible for ion channel opening to fibrillation which occurs over seconds and can lead to death. Spatial scales range from nanometre pore sizes in membrane channels and gap junctions to the metre length scale of the whole cardiovascular system in a living patient. Synchrony over these scales requires a hierarchy of control mechanisms that are governed by a single common principle: integration of structure and function. To ensure that the function of ion channels and contraction of muscle cells lead to changes in heart chamber volume, an elegant choreography of metabolic, electrical and mechanical events are executed by protein networks composed of extracellular matrix, transmembrane integrin receptors and cytoskeleton which are functionally connected across all size scales. These structural control networks are mechanoresponsive, and they process mechanical and chemical signals in a massively parallel fashion, while also serving as a bidirectional circuit for information flow. This review explores how these hierarchical structural networks regulate the form and function of living cells and tissues, as well as how microfabrication techniques can be used to probe this structural control mechanism that maintains metabolic supply, electrical activation and mechanical pumping of heart muscle. Through this process, we delineate various design principles that may be useful for engineering artificial heart tissue in the future.     

Steroid-dependent modification of Hox function drives myocyte reprogramming in the Drosophila heart

In the Drosophila larval cardiac tube, aorta and heart differentiation are controlled by the Hox genes Ultrabithorax (Ubx) and abdominal A (abdA), respectively. There is evidence that the cardiac tube undergoes extensive morphological and functional changes during metamorphosis to form the adult organ, but both the origin of adult cardiac tube myocytes and the underlying genetic control have not been established. Using in vivo time-lapse analysis, we show that the adult fruit fly cardiac tube is formed during metamorphosis by the reprogramming of differentiated and already functional larval cardiomyocytes, without cell proliferation. We characterise the genetic control of the process, which is cell autonomously ensured by the modulation of Ubx expression and AbdA activity. Larval aorta myocytes are remodelled to differentiate into the functional adult heart, in a process that requires the regulation of Ubx expression. Conversely, the shape, polarity, function and molecular characteristics of the surviving larval contractile heart myocytes are profoundly transformed as these cells are reprogrammed to form the adult terminal chamber. This process is mediated by the regulation of AbdA protein function, which is successively required within these persisting myocytes for the acquisition of both larval and adult differentiated states. Importantly, AbdA specificity is switched at metamorphosis to induce a novel genetic program that leads to differentiation of the terminal chamber. Finally, the steroid hormone ecdysone controls cardiac tube remodelling by impinging on both the regulation of Ubx expression and the modification of AbdA function. Our results shed light on the genetic control of one in vivo occurring remodelling process, which involves a steroid-dependent modification of Hox expression and function.     

Resident progenitors,not exogenous migratory cells,generate the majority of visceral mesothelium in organogenesis

Historically, analyses of mesothelial differentiation have focused on the heart where a highly migratory population of progenitors originating from a localized “extrinsic” source moves to and over the developing organ. This model long stood alone as the paradigm for generation of this cell type. Here, using chick/quail chimeric grafting and subsequent identification of mesothelial cell populations, we demonstrate that a different mechanism for the generation of mesothelia exists in vertebrate organogenesis. In this newly discovered model, mesothelial progenitors are intrinsic to organs of the developing digestive and respiratory systems. Additionally, we demonstrate that the early heart stands alone in its ability to recruit an entirely exogenous mesothelial cell layer during development. Thus, the newly identified “organ intrinsic” model of mesotheliogenesis appears to predominate while the long-studied cardiac model of mesothelial development may be the outlier.     

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this "deconditioning response" could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of -6 degrees head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15-0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate x stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05-0.15 Hz) power of systolic BP variability decreased after bed rest (-22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.     

A differentiable,periodic function for pulsatile cardiac output based on heart rate and stroke volume

Many mathematical models of human hemodynamics, particularly those which describe pressure and flow pulses throughout the circulatory system, require as specified input a modeling function which describes cardiac output in terms of volume per unit time. To be realistic, this cardiac output function should capture, to the greatest extent possible, all relevant features observed in measured physical data. For model analysis purposes, it is also highly desirable to have a model function that is continuous, differentiable, and periodic. This paper addresses both classes of needs by developing such a function. Physically, the present function provides an accurate model for flow into the ascending aorta. It is completely specified by a minimal number of standard input parameters associated with left ventricle dynamics, including heart rate, mean cardiac output, and an estimation of the peak-to-mean flow ratio. Analytically, it can be expressed as a product of two continuous, differentiable and periodic factors. Further, the Fourier expansion of this model function is shown to be a finite Fourier series, and explicit closed-form expressions are given for the non-zero coefficients in this series.     

Adding insult to injury - Inflammation at the heart of cardiac fibrosis

The fibrotic response has evolutionary worked in tandem with the inflammatory response to facilitate healing following injury or tissue destruction as a result of pathogen clearance. However, excessive inflammation and fibrosis are key pathological drivers of organ tissue damage. Moreover, fibrosis can occur in several conditions associated with chronic inflammation that are not directly caused by overt tissue injury or infection. In the heart, in particular, fibrotic adverse cardiac remodeling is a key pathological driver of cardiac dysfunction in heart failure. Cardiac fibroblast activation and immune cell activation are two mechanistic domains necessary for fibrotic remodeling in the heart, and, independently, their contributions to cardiac fibrosis and cardiac inflammation have been studied and reviewed thoroughly. The interdependence of these two processes, and how their cellular components modulate each other's actions in response to different cardiac insults, is only recently emerging. Here, we review recent literature in cardiac fibrosis and inflammation and discuss the mechanisms involved in the fibrosis-inflammation axis in the context of specific cardiac stresses, such as myocardial ischemia, and in nonischemic heart conditions. We discuss how the search for anti-inflammatory and anti-fibrotic therapies, so far unsuccessful to date, needs to be based on our understanding of the interdependence of immune cell and fibroblast activities. We highlight that in addition to the extensively reviewed role of immune cells modulating fibroblast function, cardiac fibroblasts are central participants in inflammation that may acquire immune like cell functions. Lastly, we review the gut-heart axis as an example of a novel perspective that may contribute to our understanding of how immune and fibrotic modulation may be indirectly modulated as a potential area for therapeutic research.     

Genetic steps to organ laterality in zebrafish

All internal organs are asymmetric along the left-right axis. Here we report a genetic screen to discover mutations which perturb organ laterality. Our particular focus is upon whether, and how, organs are linked to each other as they achieve their laterally asymmetric positions. We generated mutations by ENU mutagenesis and examined F3 progeny using a cocktail of probes that reveal early primordia of heart, gut, liver and pancreas. From the 750 genomes examined, we isolated seven recessive mutations which affect the earliest left-right positioning of one or all of the organs. None of these mutations caused discernable defects elsewhere in the embryo at the stages examined. This is in contrast to those mutations we reported previously (Chen et al., 1997) which, along with left-right abnormalities, cause marked perturbation in gastrulation, body form or midline structures. We find that the mutations can be classified on the basis of whether they perturb relationships among organ laterality. In Class 1 mutations, none of the organs manifest any left-right asymmetry. The heart does not jog to the left and normally leftpredominant BMP4 in the early heart tube remains symmetric. The gut tends to remain midline. There frequently is a remarkable bilateral duplication of liver and pancreas. Embryos with Class 2 mutations have organotypic asymmetry but, in any given embryo, organ positions can be normal, reversed or randomized. Class 3 reveals a hitherto unsuspected gene that selectively affects laterality of heart. We find that visceral organ positions are predicted by the direction of the preceding cardiac jog. We interpret this as suggesting that normally there is linkage between cardiac and visceral organ laterality. Class 1 mutations, we suggest, effectively remove the global laterality signals, with the consequence that organ positions are effectively symmetrical. Embryos with Class 2 mutations do manifest linkage among organs, but it may be reversed, suggesting that the global signals may be present but incorrectly orientated in some of the embryos. That laterality decisions of organs may be independently perturbed, as in the Class 3 mutation, indicates that there are distinctive pathways for reception and organotypic interpretation of the global signals.     

Decreased Autophagy Contributes to Myocardial Dysfunction in Rats Subjected to Nonlethal Mechanical Trauma

Autophagy is important in cells for removing damaged organelles, such as mitochondria. Insufficient autophagy plays a critical role in tissue injury and organ dysfunction under a variety of pathological conditions. However, the role of autophagy in nonlethal traumatic cardiac damage remains unclear. The aims of the present study were to investigate whether nonlethal mechanical trauma may result in the change of cardiomyocyte autophagy, and if so, to determine whether the changed myocardial autophagy may contribute to delayed cardiac dysfunction. Male adult rats were subjected to nonlethal traumatic injury, and cardiomyocyte autophagy, cardiac mitochondrial function, and cardiac function in isolated perfused hearts were detected. Direct mechanical traumatic injury was not observed in the heart within 24 h after trauma. However, cardiomyocyte autophagy gradually decreased and reached a minimal level 6 h after trauma. Cardiac mitochondrial dysfunction was observed by cardiac radionuclide imaging 6 h after trauma, and cardiac dysfunction was observed 24 h after trauma in the isolated perfused heart. These were reversed when autophagy was induced by administration of the autophagy inducer rapamycin 30 min before trauma. Our present study demonstrated for the first time that nonlethal traumatic injury caused decreased autophagy, and decreased autophagy may contribute to post-traumatic organ dysfunction. Though our study has some limitations, it strongly suggests that cardiac damage induced by nonlethal mechanical trauma can be detected by noninvasive radionuclide imaging, and induction of autophagy may be a novel strategy for reducing posttrauma multiple organ failure.     

The left ventricle proteome differentiates middle-aged and old left ventricles in mice

Middle-aged and old left ventricles (LVs) are structurally and functionally very similar. Compared to a young LV, both show increased wall thickness and increased cavity size, with preserved cardiac function. However, when a stressor such as myocardial infarction occurs, striking differences are revealed between young and old LVs and there is a marked reduction in survival rates for the old group. The objective of this study was to investigate the proteomic basis of age-related changes in the LV of male mice in order to identify proteins that are differentially expressed between middle-aged and old groups and to gain mechanistic insight into effects of aging on the unstressed heart. Young (3 months old; n = 6), middle-aged (MA; 15 months old; n = 6), and old (23 months old; n = 5) LVs were examined by echocardiography, homogenized, and separated into soluble and insoluble protein fractions using differential extraction. We found that the LV mass-to-tibia ratio increased from 6.4 +/- 0.2 mg/mm in young to 11.0 +/- 0.6 and 10.1 +/- 0.7 mg/mm in MA and old, respectively (both p < 0.05 vs young), which was caused by increases in both LV wall thickness and volume. Using two-dimensional gel electrophoresis, we detected age-related alterations in the levels of 73 proteins (all p < 0.05). Among these proteins were mortalin, peroxiredoxin 3, epoxide hydrolase, and the superoxide dismutases SOD-1 (Cu/ZnSOD) and SOD-2 (MnSOD), which have been previously associated with aging and/or cardiovascular disease. Together, these results reveal proteomic changes that occur in the LV with age. The proteins identified here may be useful markers of cardiac aging and may help in deducing mechanisms to explain the inability of the old heart to withstand challenge.