Clinical Study to Evaluate Mavacamten (MYK-461) in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy

Key Inclusion Criteria: * Age 18 and greater, body weight ≥ 45kg * Has adequate acoustic windows to enable accurate transthoracic echocardiograms (TTEs) * Diagnosed with oHCM consistent with current American College of Cardiology Foundation/American Heart Association and European Society of Cardiology guidelines and satisfy both criteria: * Has documented left ventricular ejection fraction (LVEF) ≥55% * NYHA Class II or III * Has documented oxygen saturation at rest ≥90% at Screening * Is able to perform an upright CPET and has a respiratory exchange ratio (RER) ≥1.0 at Screening per central reading Key Exclusion Criteria: * Known infiltrative or storage disorder causing cardiac hypertrophy that mimics oHCM, such as Fabry disease, amyloidosis, or Noonan syndrome with LV hypertrophy * History of syncope or sustained ventricular tachyarrhythmia with exercise within 6 months prior to Screening * History of resuscitated sudden cardiac arrest (at any time) or known history of appropriate implantable cardioverter defibrillator (ICD) discharge for life-threatening ventricular arrhythmia within 6 months prior to Screening * Paroxysmal, intermittent atrial fibrillation with atrial fibrillation present at Screening * Persistent or permanent atrial fibrillation not on anticoagulation for at least 4 weeks prior to Screening and/or not adequately rate controlled within 6 months prior to Screening * Treatment (within 14 days prior to Screening) or planned treatment during the study with disopyramide or ranolazine * Treatment (within 14 days prior to Screening) or planned treatment during the study with a combination of β-blockers and calcium channel blockers * LVOT gradient with Valsalva maneuver \<30 mmHg at Screening * Has been successfully treated with invasive septal reduction (surgical myectomy or percutaneous alcohol septal ablation \[ASA\]) within 6 months prior to Screening or plans to have either of these treatments during the study * ICD placement within 2 months prior to Screening or planned ICD placement during the study * Has a history or evidence of any other clinically significant disorder, condition, or disease that, in the opinion of the investigator, would pose a risk to participant safety or interfere with the study evaluation, procedures, or completion * Prior treatment with cardiotoxic agents such as doxorubicin or similar