Information Mavacamten (MYK-461) Mavacamten (MYK-461, SAR439152) is a small-molecule modulator of cardiac myosin that targets the underlying sarcomere hypercontractility of hypertrophic cardiomyopathy (HCM), one of the most prevalent heritable cardiovascular disorders. In vitro MYK-461 primarily reduces the steady-state ATPase activity by inhibiting the rate of phosphate release of β-cardiac myosin-S1. MYK-461 modulates multiple steps of the myosin chemomechanical cycle. In addition to decreasing the rate-limiting step of the cycle (phosphate release), MYK-461 reduces the number of myosin-S1 heads that can interact with the actin thin filament during transition from the weakly to the strongly bound state without affecting the intrinsic rate. MYK-461 also decreases the rate of myosin binding to actin in the ADP-bound state and the ADP-release rate from myosin-S1 alone. In vivo Early, chronic administration of MYK-461 suppresses the development of ventricular hypertrophy, cardiomyocyte disarray, and myocardial fibrosis and attenuates hypertrophic and profibrotic gene expression in mice harboring heterozygous human mutations in the myosin heavy chain.