Genetic mutations in myosin, the motor protein that powers the heartbeat, are linked to inherited hypertrophic and dilated cardiomyopathies. Mavacamten and omecamtiv mecarbil are therapeutic, myosin-targeted drugs designed to treat these myopathies, but their mechanism of action has remained unclear. Using single-particle cryo-EM, we determined near-atomic resolution structures of wild-type, mavacamten-bound, and omecamtiv mecarbil-bound myosin molecules. Across all conditions, we observe two distinct, alternate conformations of myosin, not previously reported. We show how mavacamten stabilizes one conformation by reinforcing key electrostatic interfaces in the molecule, whereas omecamtiv mecarbil weakens these interfaces, favoring the second structure. This remodeling elucidates previously unclear allosteric mechanisms through which these drugs either inhibit or enhance myosin activity, countering the deleterious impacts of disease. These findings reveal how drugs modulate myosin structure to control cardiac contractility.