Aberrant intracellular Ca 2+ regulation is believed to contribute to the development of cardiomyopathy in Duchenne muscular dystrophy. Here, we tested whether inhibition of protein kinase A (PKA) phosphorylation of ryanodine receptor type 2 (RyR2) prevents dystrophic cardiomyopathy by reducing SR Ca 2+ leak in the mdx mouse model of Duchenne muscular dystrophy. mdx mice were crossed with RyR2-S2808A mice, in which PKA phosphorylation site S2808 on RyR2 is inactivated by alanine substitution. Compared with mdx mice that developed age-dependent heart failure, mdx-S2808A mice exhibited improved fractional shortening and reduced cardiac dilation. Whereas application of isoproterenol severely depressed cardiac contractility and caused 95% mortality in mdx mice, contractility was preserved with only 19% mortality in mdx-S2808A mice. SR Ca 2+ leak was greater in ventricular myocytes from mdx than mdx-S2808A mice. Myocytes from mdx mice had a higher incidence of isoproterenol-induced diastolic Ca 2+ release events than myocytes from mdx-S2808A mice. Thus, inhibition of PKA phosphorylation of RyR2 reduced SR Ca 2+ leak and attenuated cardiomyopathy in mdx mice, suggesting that enhanced PKA phosphorylation of RyR2 at S2808 contributes to abnormal Ca 2+ homeostasis associated with dystrophic cardiomyopathy.calcium | cardiomyopathy | dystrophin | ryanodine receptor | sarcoplasmic reticulum