Phase 3 Trial to Evaluate the Efficacy and Safety of Aficamten Compared to Placebo in Adults With Symptomatic oHCM

Key Inclusion Criteria: * Males and females between 18 and 85 years of age, inclusive, at screening. * Body mass index \<35 kg/m2. * Diagnosed with HCM per the following criteria: * Has LV hypertrophy and non-dilated LV chamber in the absence of other cardiac disease and * Has an end-diastolic LV wall thickness as measured by the echocardiography core laboratory of: * ≥15 mm in one or more myocardial segments OR * ≥13 mm in one or more wall segments and a known-disease-causing gene mutation or positive family history of HCM * Has resting LVOT-G ≥30 mmHg and post-Valsalva LVOT G ≥50 mmHg during screening as determined by the echocardiography core laboratory. * LVEF ≥60% at screening as determined by the echocardiography core laboratory. * New York Heart Association (NYHA) Functional Class II or III at screening. * Hemoglobin ≥10g/dL at screening. * Respiratory exchange ratio (RER) ≥1.05 and pVO2 ≤90% predicted on the screening CPET per the core laboratory. * Patients on beta-blockers, verapamil, diltiazem, or disopyramide should have been on stable doses for \>6 weeks prior to randomization and anticipate remaining on the same medication regimen during the trial. Patients treated with disopyramide must also be concomitantly treated with a beta blocker and/or calcium channel blocker. Key Exclusion Criteria: * Known or suspected infiltrative, genetic or storage disorder causing cardiac hypertrophy that mimics oHCM (eg, Noonan syndrome, Fabry disease, amyloidosis). * Significant valvular heart disease (per investigator judgment). * Moderate-severe valvular aortic stenosis. * Moderate-severe mitral regurgitation not due to systolic anterior motion of the mitral valve. * History of LV systolic dysfunction (LVEF \<45%) or stress cardiomyopathy at any time during their clinical course. * Inability to exercise on a treadmill or bicycle (eg, orthopedic limitations). * Has been treated with septal reduction therapy (surgical myectomy or percutaneous alcohol septal ablation) or has plans for either treatment during the trial period. * Documented paroxysmal atrial fibrillation during the screening period. * Paroxysmal or permanent atrial fibrillation is only excluded IF: * rhythm restoring treatment (eg, direct-current cardioversion, atrial fibrillation ablation procedure, or antiarrhythmic therapy) has been required ≤6 months prior to screening. * rate control and anticoagulation have not been achieved for at least 6 months prior to screening. * History of syncope or sustained ventricular tachyarrhythmia with exercise within 6 months prior to screening. * Has received prior treatment with CK-3773274 or mavacamten.