Abstract Introduction Mavacamten, a cardiac myosin inhibitor, has demonstrated positive outcomes in left ventricular outflow tract (LVOT) gradient reduction and improvements of symptoms and function in Chinese patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM) in EXPLORER-CN. This exploratory analysis aimed to evaluate the effect of mavacamten on echocardiographic measures of cardiac structure and function and its relationship with other clinical biomarkers. Methods Key echocardiographic parameters acquired over 30 weeks from 81 patients (n = 54 on mavacamten and n = 27 on placebo) were assessed in a central laboratory. Results At 30 weeks, greater improvements in measures of diastolic function were observed with mavacamten versus placebo, including lateral E/e′ (least-squares mean [LSM] change from baseline [CFB] − 5.1 vs. 0.6; between-group LSM difference − 5.7; 95% confidence interval [CI] − 7.6 to − 3.7), septal E/e′ (LSM CFB − 6.0 vs. − 0.3; between-group LSM difference − 5.7; 95% CI − 7.8 to − 3.7), and left atrial volume index (LAVI) (LSM CFB − 11.7 vs. − 3.5 ml/m2; between-group LSM difference − 8.2; 95% CI − 12.0 to − 4.4) (nominal p