Two Classes of Myosin Inhibitors, Para-nitroblebbistatin and Mavacamten, Stabilize β-Cardiac Myosin in Different Structural and Functional States

•In relaxed cardiac muscle, some myosins exist in energy-sparing off states.•This reserve pool of myosins can be recruited under increased cardiac demand.•Disruption of these off states enhances contractility and impairs cardiac relaxation.•As a therapeutic molecule, mavacamten restores myosin into these off states.•Blebbistatin stabilizes myosin in different off states, compared to mavacamten.•Hence, different molecules can modulate myosin structure and function differently.