Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease characterized by marked increase in cardiac mass caused by proliferation/hypertrophy of several cell types (myocytes, fibroblasts, smooth muscle cells, and endothelial cells). There is often associated left ventricular (LV) diastolic dysfunction and myocardial ischemia. The severity of the LV hypertrophy, diastolic dysfunction, and myocardial ischemia are important determinants of clinical course. In several animal models of LV hypertrophy, calcineurin has been implicated in the development of myocardial hypertrophy, leading to cardiac dilatation and failure. Inhibitors of calcineurin (Cyclosporin A and FK506) have been shown to prevent the development of cardiac hypertrophy in these animal models, where cardiac hypertrophy is related to sarcomeric dysfunction. We propose to study the ability of Cyclosporin A (CsA) to reduce LV mass, and to improve symptoms, LV diastolic function, and myocardial perfusion in HCM caused by sarcomeric gene mutations.