Abstract: Disclosed herein are methods of treatment comprising administering a therapeutically effective amount of a myosin modulator or a pharmaceutically acceptable salt thereof to a subject in need thereof and diagnostic methods useful in connection with those treatments. Due to observations unfolding in clinical trials with mavacamten and with mavacamten and other myosin inhibitors in the pre-clinical setting, new insights into how myosin inhibitors can be used beneficially to impact the disease state of HCM and other diseases are provided herein.