--- - |2 In this study, we revealed the effect of ranolazine to attenuate pressure overload‐induced cardiac hypertrophy and heart failure in mice by reducing Na+ accumulation and Ca 2+ overload, normalizing SR leak. The Ca 2+‐dependent Ca 2+/calmodulin (CaM)/CaMKII/MEF2D and CaM/CaMKII/calcineurin/nuclear factor of activated T‐cells hypertrophic pathways and endoplasmic reticulum (ER) stress were triggered by pressure overload and were inhibited by ranolazine. Abstract Background Cardiac hypertrophy and heart failure are characterized by increased late sodium current and abnormal Ca2+ handling. Ranolazine, a selective inhibitor of the late sodium current, can reduce sodium accumulation and Ca 2+ overload. In this study, we investigated the effects of ranolazine on pressure overload‐induced cardiac hypertrophy and heart failure in mice. Methods and Results Inhibition of late sodium current with the selective inhibitor ranolazine suppressed cardiac hypertrophy and fibrosis and improved heart function assessed by echocardiography, hemodynamics, and histological analysis in mice exposed to chronic pressure overload induced by transverse aortic constriction (TAC). Ca2+ imaging of ventricular myocytes from TAC mice revealed both abnormal SR Ca 2+ release and increased SR Ca 2+ leak. Ranolazine restored aberrant SR Ca 2+ handling induced by pressure overload. Ranolazine also suppressed Na + overload induced in the failing heart, and restored Na +‐induced Ca 2+ overload in an sodium‐calcium exchanger (NCX)‐dependent manner. Ranolazine suppressed the Ca 2+‐dependent calmodulin (CaM)/CaMKII/myocyte enhancer factor‐2 (MEF2) and CaM/CaMKII/calcineurin/nuclear factor of activated T‐cells (NFAT) hypertrophy signaling pathways triggered by pressure overload. Pressure overload also prolonged endoplasmic reticulum (ER) stress leading to ER‐initiated apoptosis, while inhibition of late sodium current or NCX relieved ER stress and ER‐initiated cardiomyocyte apoptosis. Conclusions Our study demonstrates that inhibition of late sodium current with ranolazine improves pressure overload‐induced cardiac hypertrophy and systolic and diastolic function by restoring Na+ and Ca 2+ handling, inhibiting the downstream hypertrophic pathways and ER stress. Inhibition of late sodium current may provide a new treatment strategy for cardiac hypertrophy and heart failure. - 'Journal of Cellular Physiology, EarlyView. '