Sarcomeres are the fundamental contractile units of striated muscle. The functional roles of the cardiac-specific myosin heavy chains, MYH6 (α myosin II) and MYH7 (β myosin II) during sarcomere assembly remain controversial. To address this, we utilized a selective MYH7 inhibitor, mavacamten, in combination with siRNA-mediated knockdown of MYH6 or MYH7 in human induced pluripotent stem cell-derived cardiomyocytes (hiCMs). Our results demonstrate that sarcomere assembly proceeds when either MYH6 or MYH7 is independently depleted, suggesting functional redundancy. However, pharmacological inhibition of MYH7 contractility by mavacamten disrupts sarcomere assembly in a concentration-dependent manner. Sensitivity to mavacamten correlated with the relative abundance of MYH6 and MYH7: sarcomere assembly by MYH7-enriched (i.e., MYH6-depleted) hiCMs was more sensitive to mavacamten (IC