The power athlete

BRADYCARDIA IN ATHLETES: DOES THE TYPE OF SPORT MAKE ANY DIFFERENCE? – A SYSTEMATIC REVIEW

ABSTRACT Bradycardia in athletes can range from moderate to severe, and the factors that contribute to slow heart rate are complex. Studies investigating the mechanisms associated with this condition are controversial, and may be linked to the form of exercise practiced. A systematic literature review was conducted to discuss bradycardia mechanisms in athletes who practice different forms of sport. The databases consulted were Pubmed (MEDLINE), Clinical Trials, Cochrane, Scopus, Web of Science, SciELO, Sport Discus and PEDro. The search included English language articles published up to January 2019, that evaluated athletes who practiced different forms of sport. One hundred and ninety-three articles were found, ten of which met the inclusion criteria, with 1549 male and female athletes who practiced diverse forms of sport. Resting heart rate and cardiac structure were studied in association with the form of sport practiced, through heart rate variability, electrocardiogram, echocardiogram and pharmacological blockade. The studies suggest that a slow resting heart rate cannot be explained by increased vagal modulation alone, but also includes changes in cardiac structure. According to the studies, different sports seem to produce different cardiac responses, and the bradycardia found in athletes can be explained by non-autonomic and autonomic mechanisms, depending on the type of effort or the form of sport practiced. However, the mechanism underlying the slow heart rate in each form of sport is still unclear. Level of evidence II; Prognostic studies - Investigating the effect of a patient characteristic on the outcome of disease.

Associations of Resistance Exercise with Cardiovascular Disease Morbidity and Mortality

PURPOSE

Resistance exercise (RE) can improve many cardiovascular disease (CVD) risk factors, but specific data on the effects on CVD events and mortality are lacking. We investigated the associations of RE with CVD and all-cause mortality and further examined the mediation effect of body mass index (BMI) between RE and CVD outcomes.

METHODS

We included 12,591 participants (mean age, 47 yr) who received at least two clinical examinations 1987-2006. RE was assessed by a self-reported medical history questionnaire.

RESULTS

During a mean follow-up of 5.4 and 10.5 yr, 205 total CVD events (morbidity and mortality combined) and 276 all-cause deaths occurred, respectively. Compared with no RE, weekly RE frequencies of one, two, three times or total amount of 1-59 min were associated with approximately 40%-70% decreased risk of total CVD events, independent of aerobic exercise (AE) (all P values <0.05). However, there was no significant risk reduction for higher weekly RE of more than four times or ≥60 min. Similar results were observed for CVD morbidity and all-cause mortality. In the stratified analyses by AE, weekly RE of one time or 1-59 min was associated with lower risks of total CVD events and CVD morbidity regardless of meeting the AE guidelines. Our mediation analysis showed that RE was associated with the risk of total CVD events in two ways: RE had a direct U-shaped association with CVD risk (P value for quadratic trend <0.001) and RE indirectly lowered CVD risk by decreasing BMI.

CONCLUSION

Even one time or less than 1 h·wk of RE, independent of AE, is associated with reduced risks of CVD and all-cause mortality. BMI mediates the association of RE with total CVD events.

Strength Training and All-Cause, Cardiovascular Disease, and Cancer Mortality in Older Women: A Cohort Study

BACKGROUND

Few data exist on the association between strength training and mortality rates. We sought to examine the association between strength training and all-cause, cardiovascular disease, and cancer mortality.

METHODS AND RESULTS

Beginning in 2001 to 2005, 28 879 women throughout the United States (average baseline age, 62.2 years) from the Women's Health Study who were free of cardiovascular disease, diabetes mellitus, and cancer reported their physical activities, including strength training. During follow-up (average, 12.0 years) through 2015, investigators documented 3055 deaths (411 from cardiovascular disease and 748 from cancer). After adjusting for covariables, including aerobic activity, time in strength training showed a quadratic association with all-cause mortality (P=0.36 for linear trend; P<0.001 for quadratic trend); hazard ratios across 5 categories of strength training (0, 1-19, 20-59, 60-149, and ≥150 min/wk) were 1.0 (referent), 0.73 (95% confidence interval, 0.65-0.82), 0.71 (0.62-0.82), 0.81 (0.67-0.97), and 1.10 (0.77-1.56), respectively. A significant quadratic association was also observed for cardiovascular disease death (P=0.007) but not cancer death (P=0.41). Spline models also indicated a J-shaped nonlinear association for all-cause mortality (P=0.020); the point estimates of hazard ratios were <1.00 for 1 to 145 min/wk of strength training, compared with 0 min/wk, whereas hazard ratios were >1.00 for ≥146 min/wk of strength training. However, confidence intervals were wide at higher levels of strength training.

CONCLUSIONS

Time in strength training showed a J-shaped association with all-cause mortality in older women. A moderate amount of time in strength training seemed beneficial for longevity, independent of aerobic activity; however, any potential risk with more time (≈≥150 min/wk) should be further investigated.

Whole-body strength training with Huber Motion Lab and traditional strength training in cardiac rehabilitation: A randomized controlled study

BACKGROUND

Isometric strengthening has been rarely studied in patients with coronary heart disease (CHD), mainly because of possible potential side effects and lack of appropriate and reliable devices.

OBJECTIVE

We aimed to compare 2 different modes of resistance training, an isometric mode with the Huber Motion Lab (HML) and traditional strength training (TST), in CHD patients undergoing a cardiac rehabilitation program.

DESIGN

We randomly assigned 50 patients to HML or TST. Patients underwent complete blinded evaluation before and after the rehabilitation program, including testing for cardiopulmonary exercise, maximal isometric voluntary contraction, endothelial function and body composition.

RESULTS

After 4 weeks of training (16 sessions), the groups did not differ in body composition, anthropometric characteristics, or endothelial function. With HML, peak power output (P=0.035), maximal heart rate (P<0.01) and gain of force measured in the chest press position (P<0.02) were greater after versus before training.

CONCLUSION

Both protocols appeared to be well tolerated, safe and feasible for these CHD patients. A training protocol involving 6s phases of isometric contractions with 10s of passive recovery on an HML device could be safely implemented in rehabilitation programs for patients with CHD and improve functional outcomes.

Aerobic Fitness Level Affects Cardiovascular and Salivary Alpha Amylase Responses to Acute Psychosocial Stress

Background

Good physical fitness seems to help the individual to buffer the potential harmful impact of psychosocial stress on somatic and mental health. The aim of the present study is to investigate the role of physical fitness levels on the autonomic nervous system (ANS; i.e. heart rate and salivary alpha amylase) responses to acute psychosocial stress, while controlling for established factors influencing individual stress reactions.

Methods

The Trier Social Stress Test for Groups (TSST-G) was executed with 302 male recruits during their first week of Swiss Army basic training. Heart rate was measured continuously, and salivary alpha amylase was measured twice, before and after the stress intervention. In the same week, all volunteers participated in a physical fitness test and they responded to questionnaires on lifestyle factors and personal traits. A multiple linear regression analysis was conducted to determine ANS responses to acute psychosocial stress from physical fitness test performances, controlling for personal traits, behavioural factors, and socioeconomic data.

Results

Multiple linear regression revealed three variables predicting 15 % of the variance in heart rate response (area under the individual heart rate response curve during TSST-G) and four variables predicting 12 % of the variance in salivary alpha amylase response (salivary alpha amylase level immediately after the TSST-G) to acute psychosocial stress. A strong performance at the progressive endurance run (high maximal oxygen consumption) was a significant predictor of ANS response in both models: low area under the heart rate response curve during TSST-G as well as low salivary alpha amylase level after TSST-G. Further, high muscle power, non-smoking, high extraversion, and low agreeableness were predictors of a favourable ANS response in either one of the two dependent variables.

Conclusions

Good physical fitness, especially good aerobic endurance capacity, is an important protective factor against health-threatening reactions to acute psychosocial stress.

Efficacy of Ashwagandha (Withania somnifera [L.] Dunal) in improving cardiorespiratory endurance in healthy athletic adults

Introduction:

Ashwagandha (Withania somnifera [L.] Dunal) has been traditionally used for various actions ranging from vitalizer, improve endurance and stamina, promote longevity, improve immunity, and male and female fertility. However, clinical studies are needed to prove the clinical efficacy of this herb, especially in cardiovascular endurance and physical performance.

Aims:

This prospective, double-blind, randomized, and placebo-controlled study evaluated the efficacy of Ashwagandha roots extract in enhancing cardiorespiratory endurance and improving the quality of life (QOL) in 50 healthy male/female athletic adults.

Materials and Methods:

Cardiorespiratory endurance was assessed by measuring the oxygen consumption at peak physical exertion (VO₂ max) levels during a 20 m shuttle run test. The World Health Organization self-reported QOL questionnaire (physical health, psychological health, social relationships, and environmental factors) was used to assess the QOL. Student's t-test was used to compare the differences in a mean and change from baseline VO₂ max levels, whereas Wilcoxon signed-rank test was used to assess changes in QOL scores from baseline in the two groups.

Results:

There was a greater increase from baseline (P < 0.0001) in the mean VO₂ max with KSM-66 Ashwagandha (n = 24) compared to placebo (n = 25) at 8 weeks (4.91 and 1.42, respectively) and at 12 weeks (5.67 and 1.86 respectively). The QOL scores for all subdomains significantly improved to a greater extent in the Ashwagandha group at 12 weeks compared to placebo (P < 0.05).

Conclusion:

The findings suggest that Ashwagandha root extract enhances the cardiorespiratory endurance and improves QOL in healthy athletic adults.

Aerobic exercise training promotes physiological cardiac remodeling involving a set of microRNAs

Left ventricular (LV) hypertrophy is an important physiological compensatory mechanism in response to chronic increase in hemodynamic overload. There are two different forms of LV hypertrophy, one physiological and another pathological. Aerobic exercise induces beneficial physiological LV remodeling. The molecular/cellular mechanisms for this effect are not totally known, and here we review various mechanisms including the role of microRNA (miRNA). Studies in the heart, have identified antihypertrophic miRNA-1, -133, -26, -9, -98, -29, -378, and -145 and prohypertrophic miRNA-143, -103, -130a, -146a, -21, -210, -221, -222, -27a/b, -199a/b, -208, -195, -499, -34a/b/c, -497, -23a, and -15a/b. Four miRNAs are recognized as cardiac-specific: miRNA-1, -133a/b, -208a/b, and -499 and called myomiRs. In our studies we have shown that miRNAs respond to swimming aerobic exercise by 1) decreasing cardiac fibrosis through miRNA-29 increasing and inhibiting collagen, 2) increasing angiogenesis through miRNA-126 by inhibiting negative regulators of the VEGF pathway, and 3) modulating the renin-angiotensin system through the miRNAs-27a/b and -143. Exercise training also increases cardiomyocyte growth and survival by swimming-regulated miRNA-1, -21, -27a/b, -29a/c, -30e, -99b, -100, -124, -126, -133a/b, -143, -144, -145, -208a, and -222 and running-regulated miRNA-1, -26, -27a, -133, -143, -150, and -222, which influence genes associated with the heart remodeling and angiogenesis. We conclude that there is a potential role of these miRNAs in promoting cardioprotective effects on physiological growth.

Cardiovascular responses to passive static flexibility exercises are influenced by the stretched muscle mass and the Valsalva maneuver

BACKGROUND

The respiratory pattern is often modified or even blocked during flexibility exercises, but little is known about the cardiovascular response to concomitant stretching and the Valsalva maneuver (VM) in healthy subjects.

OBJECTIVES

This study evaluated the heart rate (HR), systolic blood pressure (SBP), and rate-pressure product (RPP) during and after large and small muscle group flexibility exercises performed simultaneously with the VM.

METHODS

Asymptomatic volunteers (N = 22) with the following characteristics were recruited: age, 22 ± 3 years; weight, 73 ± 6 kg; height, 175 ± 5 cm; HR at rest, 66 ± 9 BPM; and SBP at rest, 113 ± 10 mmHg. They performed two exercises: four sets of passive static stretching for 30 s of the dorsi-flexion (DF) of the gastrocnemius and the hip flexion (HF) of the ischio-tibialis. The exercises were performed with (V+) or without (V-) the VM in a counterbalanced order. The SBP and HR were measured, and the RPP was calculated before the exercise session, at the end of each set, and during a 30-min post-exercise recovery period.

RESULTS

The within-group comparisons showed that only the SBP and RPP increased throughout the sets (p < 0.05), but no post-exercise hypotension was detected. The between-group comparisons showed that greater SBP increases were related to the VM and to a larger stretched muscle mass. Differences for a given set were identified for the HR (the HFV+ and HFV- values were higher than the DFV+ and DFV- values by approximately 12 BPM), SBP (the HFV+ value was higher than the DFV+ and DFV- values by approximately 12 to 15 mmHg), and RPP (the HFV+ value was higher than the HFV- value by approximately 2000 mmHGxBPM, and the HFV+ value was higher than the DFV+ and DFV- values by approximately 4000 mmHGxBPM).

CONCLUSION

Both the stretched muscle mass and the VM influence acute cardiovascular responses to multiple-set passive stretching exercise sessions.

Normal resting electrocardiographic variants in young athletes

With a growing awareness of the tragedy of sudden cardiac arrest (SCA) in young athletes, more extensive pre-participation examinations are being performed prior to competitive sport participation. In addition to a history and physical, young athletes often have a 12-lead resting electrocardiogram (ECG) to better identify heart disease associated with SCA. Complicating this process is that certain "abnormal" resting ECG findings are considered normal variants in healthy children and young adults. The ability to recognize these normal variants is often useful in preventing excessive referral of patients to cardiologists for evaluation of resting ECG's that are benign variations of normal and in making sound decisions regarding appropriate clearance to exercise. This review describes these normal variants.

KEYWORDS

normal variants; early repolarization; athlete's heart.

A broken heart — or anguish in top-sport in antiquity

Cardiovascular disease is a major determinant of sudden death. Nevertheless the impact of autonomic dysregulation is grossly underestimated not to say ignored. The limited life expectancy of retired gladiators is a fine example of the interactive influence of an occupational- and socio-cultural hazard at the time. Possibly the fate of retired athletes in antiquity is sealed by autonomic dysregulation, cardiac adaptation and noxious exposure in fatal interaction. Observations like these could be helpful in the understanding of complex pathofysiological mechanisms, and may have implications in medical practice.

Left ventricular diastolic function in trained male weight lifters at rest and during isometric exercise

Individuals involved in intense resistance training present with increased absolute left ventricular (LV) wall thickness and mass and show good systolic responses to isometric exercise. There is no consensus regarding diastolic features and no available information regarding diastolic function in athletes during isometric exertion itself. Therefore, the main aim of this study was to assess diastolic LV function at baseline and during exercise in athletes. The population consisted of 96 men (mean age 29 +/- 7 years): 48 weight lifters who trained for 15 to 20 hours/week and 48 sedentary men. All weight lifters had been active for >6 years, including the 6 months before the study. Ultrasound was performed using a commercially available Doppler echocardiographic system. Isometric exercise was performed in the supine position using a standard 2-hand bar dynamometer. The man end-diastolic volumes at rest were 97 +/- 6 ml in sedentary subjects and 101 +/- 5 ml in weight lifters, increasing to 100 +/- 6 and 118 +/- 11 ml during exercise (p = 0.06 and p <0.01, respectively). End-systolic volumes at rest were similar in the 2 groups, showing significantly greater reductions during exercise in the weight lifters. The mean absolute LV mass was 167 +/- 30 g in sedentary subjects and 202 +/- 32 g in weight lifters (p <0.0001). The mean stroke volume increased from 65 +/- 7 to 86 +/- 7 ml in sedentary subjects and from 70 +/- 6 to 107 +/- 11 ml in weight lifters (intergroup significance p = 0.05 and p <0.01, respectively). A similar pattern of response was documented for the ejection fraction (i.e., significantly greater increases during exercise in weight lifters). Regarding diastolic indexes, in the weight lifters, the mean peak early velocity at rest was 68 +/- 7 cm/s, the mean acceleration rate was 1,242 +/- 176 cm/s/s, and the mean deceleration rate was 414 +/- 44 cm/s/s. All these values were significantly higher than in sedentary subjects, with further increases during exercise (p <0.0001). In weight lifters, the mean peak atrial velocity at rest was 37 +/- 6 cm/s, the mean acceleration time was 55 +/- 4 ms, the mean isovolumic relaxation time was 63 +/- 3 ms, and the mean deceleration time was 164 +/- 4 ms; these values were lower than in sedentary subjects (p <0.0001 for all). In conclusion, intense resistance training leads to enhanced LV diastolic function at rest and during isometric exercise despite the markedly increased LV mass.

Apoptosis signal-regulating kinase 1/p38 signaling pathway negatively regulates physiological hypertrophy

BACKGROUND

Mechanical stress on the heart can lead to crucially different outcomes. Physiological stimuli such as exercise cause adaptive cardiac hypertrophy, characterized by a normal cardiac structure and normal or enhanced cardiac function. Pathological stimuli such as hypertension and aortic valvular stenosis cause maladaptive cardiac remodeling and ultimately heart failure. Apoptosis signal-regulating kinase 1 (ASK1) is known to be involved in pathological cardiac remodeling, but it has not been determined whether ASK1 pathways coordinate the signaling cascade leading to physiological type cardiac growth.

METHODS AND RESULTS

To evaluate the role of ASK1 in the physiological form of cardiac growth, mice lacking ASK1 (ASK1-/-) were exercised by swimming for 4 weeks. ASK1-/- mice showed exaggerated growth of the heart accompanied by typical characteristics of physiological hypertrophy. Their swimming-induced activation of Akt, a key molecule in the signaling cascade of physiological hypertrophy, increased more than that seen in wild-type controls. The activation of p38, a downstream kinase of ASK1, was suppressed selectively in the swimming-exercised ASK1-/- mice. Furthermore, the inhibition of ASK1 or p38 activity enhanced insulin-like growth factor 1-induced protein synthesis in rat neonatal ventricular cardiomyocytes, and the treatment with a specific inhibitor of p38 resulted in enhancement of Akt activation and suppression of protein phosphatase 2A activation. The cardiac-specific p38alpha-deficient mice developed an exacerbated form of cardiac hypertrophy in response to swimming exercise.

CONCLUSIONS

These results indicate that the ASK1/p38 signaling pathway negatively regulates physiological hypertrophy.

Akt1 Is Required for Physiological Cardiac Growth

Background— Postnatal growth of the heart chiefly involves nonproliferative cardiomyocyte enlargement. Cardiac hypertrophy exists in a “physiological” form that is an adaptive response to long-term exercise training and as a “pathological” form that often is a maladaptive response to provocative stimuli such as hypertension and aortic valvular stenosis. A signaling cascade that includes the protein kinase Akt regulates the growth and survival of many cell types, but the precise role of Akt1 in either form of cardiac hypertrophy is unknown.

Methods and Results— To evaluate the role of Akt1 in physiological cardiac growth, akt1 −/− adult murine cardiac myocytes (AMCMs) were treated with IGF-1, and akt1 −/− mice were subjected to exercise training. akt1 −/− AMCMs were resistant to insulin-like growth factor-1–stimulated protein synthesis. The akt1 −/− mice were found to be resistant to swimming training–induced cardiac hypertrophy. To evaluate the role of Akt in pathological cardiac growth, akt1 −/− AMCMs were treated with endothelin-1, and akt1 −/− mice were subjected to pressure overload by transverse aortic constriction. Surprisingly, akt1 −/− AMCMs were sensitized to endothelin-1–induced protein synthesis, and akt1 −/− mice developed an exacerbated form of cardiac hypertrophy in response to transverse aortic constriction.

Conclusions— These results establish Akt1 as a pivotal regulatory switch that promotes physiological cardiac hypertrophy while antagonizing pathological hypertrophy.

Unfavorable Effects of Resistance Training on Central Arterial Compliance

Background— Reductions in the compliance of central arteries exert a number of adverse effects on cardiovascular function and disease risk. Endurance training is efficacious in increasing arterial compliance in healthy adults. We determined the effects of resistance training on carotid arterial compliance using the intervention study design.

Methods and Results— Twenty-eight healthy men 20 to 38 years old were randomly assigned to the intervention group (n=14) and the control group (n=14). Control subjects were instructed not to alter their normal activity levels throughout the study period. Intervention subjects underwent 3 supervised resistance training sessions per week for 4 months and detraining for a subsequent 4 months. The resistance training increased maximal strength in all muscle groups tested ( P <0.001). There were no significant differences in baseline arterial compliance and β-stiffness index between the intervention and control groups. In the intervention group, carotid arterial compliance decreased 19% ( P <0.05), and β-stiffness index increased 21% ( P <0.01) after resistance training. These values returned completely to the baseline levels during the detraining period. Arterial compliance did not change in the control group. In both groups, there were no significant changes in brachial and carotid blood pressure, carotid intima-media thickness, lumen diameter, and femoral arterial compliance. Changes in carotid artery compliance were significantly and negatively related to corresponding changes in left ventricular mass index ( r =−0.56, P <0.001) and left ventricular hypertrophy index ( r =−0.68, P <0.001).

Conclusions— In marked contrast to the beneficial effect of regular aerobic exercise, several months of resistance training “reduces” central arterial compliance in healthy men.

Greater age-related reductions in central arterial compliance in resistance-trained men

Reductions in the compliance of central arteries exert a number of adverse effects on systemic cardiovascular function and disease risk. Using the cross-sectional study design, we determined the relation between chronic resistance training and carotid arterial compliance. A total of 62 healthy normotensive men, 20 to 39 years of age (young) and 40 to 60 years of age (middle-aged), who were either sedentary or resistance-trained, were studied. In both activity groups, carotid arterial compliance (simultaneous ultrasound and applanation tonometry) was lower (P<0.05) in the middle-aged compared with the young men. There was no significant difference between young sedentary and resistance-trained men. In the middle-aged group, carotid arterial compliance in the resistance-trained men was approximately 30% lower (P<0.01) than their sedentary peers. Femoral artery compliance and arm pulse wave velocity (measures of peripheral artery stiffness) were not different among any groups. Left ventricular hypertrophy index (echocardiography) was greater (P<0.05) in resistance-trained compared with sedentary men and was associated with carotid arterial compliance (r=-0.35; P<0.01). We concluded that (1) resistance training is associated with the smaller central arterial compliance in healthy middle-aged men; (2) age-related reductions in arterial compliance was greater in resistance-trained men than in sedentary men; and (3) the lower arterial compliance in the resistance-trained men is associated with left ventricular hypertrophy. In marked contrast to the beneficial effect of regular aerobic exercise, the present findings are not consistent with the idea that resistance training exerts beneficial influences on arterial wall buffering functions.

Physiological effects of exercise on the cardiopulmonary system

The cardiopulmonary adaptations made to dynamic and static exercise show the amazing ability of the human body to alter physiological processes in order to meet metabolic demands. A remarkable partnership that allows individuals to maximize their abilities and obtain goals exists between the cardiovascular and pulmonary systems. The adaptations of the cardiopulmonary system depend heavily on the intensity, duration, frequency, and type of exercise being performed. Although most of this article examined dynamic and static exercise separately, the majority of individuals train using a combination of these two modes. The overall adaptations will vary with the chosen degree of each exercise mode. An appropriate exercise program allows for improvements in the cardiopulmonary system that help develop and maintain fitness levels.

RGS4 reduces contractile dysfunction and hypertrophic gene induction in Galpha q overexpressing mice

The intrinsic GTPase activity of Galpha q is low, and RGS proteins which activate GTPase are expressed in the heart; however, their functional relevance in vivo is unknown. Transgenic mice with cardiac-specific overexpression of Galpha q in myocardium exhibit cardiac hypertrophy, enhanced PKC xi membrane translocation, embryonic gene expression, and depressed cardiac contractility. We recently reported that transgenic mice with cardiac-specific expression of RGS4, a Galpha q and Galpha i GTPase activator, exhibit decreased left ventricular hypertrophy and ANF induction in response to pressure overload. To test the hypothesis that RGS4 can act as a Galpha q-specific GTPase activating protein (GAP) in the in vivo heart, dual transgenic Galpha q-40xRGS4 mice were generated to determine if RGS4 co-expression would ameliorate the Galpha q-40 phenotype. At age 4 weeks, percent fractional shortening was normalized in dual transgenic mice as was left ventricular internal dimension and posterior and septal wall thicknesses. PKC xi membrane translocation and ANF and alpha -skeletal actin mRNA levels were also normalized. Compound transgenic mice eventually developed depressed cardiac contractility that was evident by 9 weeks of age. These studies establish for the first time a role for RGS4 as a GAP for Galpha q in the in vivo heart, and demonstrate that its regulated expression can have pathophysiologic consequences.

RGS4 causes increased mortality and reduced cardiac hypertrophy in response to pressure overload

RGS family members are GTPase-activating proteins (GAPs) for heterotrimeric G proteins. There is evidence that altered RGS gene expression may contribute to the pathogenesis of cardiac hypertrophy and failure. We investigated the ability of RGS4 to modulate cardiac physiology using a transgenic mouse model. Overexpression of RGS4 in postnatal ventricular tissue did not affect cardiac morphology or basal cardiac function, but markedly compromised the ability of the heart to adapt to transverse aortic constriction (TAC). In contrast to wild-type mice, the transgenic animals developed significantly reduced ventricular hypertrophy in response to pressure overload and also did not exhibit induction of the cardiac "fetal" gene program. TAC of the transgenic mice caused a rapid decompensation in most animals characterized by left ventricular dilatation, depressed systolic function, and increased postoperative mortality when compared with nontransgenic littermates. These results implicate RGS proteins as a crucial component of the signaling pathway involved in both the cardiac response to acute ventricular pressure overload and the cardiac hypertrophic program.