A Study of Mavacamten in Non-Obstructive Hypertrophic Cardiomyopathy

The purpose of this study is to evaluate the safety, tolerability, and efficacy of mavacamten compared with placebo in participants with symptomatic non-obstructive hypertrophic cardiomyopathy (nHCM).

Inclusion Criteria * Diagnosis of HCM consistent with current American College of Cardiology Foundation/American Heart Association and European Society of Cardiology guidelines: unexplained left-ventricular hypertrophy with non-dilated ventricular chambers in the absence of other cardiac or systemic disease which can produce the required magnitude of hypertrophy of a maximal left ventricular (LV) wall thickness ≥ 15 millimeters (mm) (or ≥ 13 mm with positive family history of hypertrophic cardiomyopathy \[HCM\]) as determined by core laboratory interpretation. * Peak left ventricular outflow tract (LVOT) pressure gradient \< 30 millimeters mercury (mm Hg) at rest and \< 50 mm Hg with provocation (Valsalva maneuver and stress echocardiography). * New York Heart Association (NYHA) Class II or III. Exclusion Criteria * Known infiltrative or storage disorder causing cardiac hypertrophy that mimics non-obstructive hypertrophic cardiomyopathy (nHCM) such as Fabry disease, amyloidosis, or Noonan syndrome with LV hypertrophy. * History of unexplained syncope within 6 months prior to screening. * History of sustained ventricular tachyarrhythmia (\> 30 seconds) within 6 months prior to screening. * Other protocol-defined Inclusion/Exclusion criteria apply.