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

Inclusion Criteria: * Participants who meet all the following criteria at screening may be included in the trial: * Males and females between 18 to 85 years of age, inclusive, at screening * Body mass index \< 35 kg/m2 * Diagnosed with oHCM per the following criteria by cardiac magnetic resonance imaging (CMR) or echocardiography - * Has left ventricular (LV) hypertrophy with 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: 1. ≥ 15 mm in one or more myocardial segments OR 2. ≥ 13 mm in one or more wall segments and a known disease-causing gene mutation or positive family history of HCM * New York Heart Association (NYHA) class II or III * Has a Kansas City Cardiomyopathy Questionnaire - Clinical Summary Score (KCCQ-CSS) score of ≤ 90 at screening * Has a screening echocardiogram with the following determined by the echocardiography core laboratory: * Resting left ventricular outflow tract gradient (LVOT-G) \> 30 mm Hg and/or post-Valsalva LVOT-G ≥ 50 mmHg at screening AND * LVEF ≥ 60% * Hemoglobin ≥ 10g/dL * Respiratory exchange ratio (RER) ≥ 1.05 and peak oxygen uptake (pVO2) \< 100% predicted on the screening cardiopulmonary exercise testing (CPET) per the core laboratory * Patients previously exposed to mavacamten are allowed to participate but must be off mavacamten for at least 8 weeks Exclusion Criteria: * Any of the following criteria will exclude potential participants from the trial: * Medical indication for either beta blocker or calcium-channel blockers prohibiting drug discontinuation other than oHCM * History of intolerance or medical contraindication to beta blocker therapy * Resting Systolic Blood Pressure (SBP) of \> 160 mmHg * Resting heart rate of \> 100 bpm * Significant valvular heart disease 1. Moderate-severe valvular aortic stenosis or fixed subaortic obstruction 2. Mitral regurgitation not due to systolic anterior motion of the mitral valve (per Investigator judgment) * Known or suspected infiltrative, genetic or storage disorder causing cardiac hypertrophy that mimics oHCM (eg, Noonan syndrome, Fabry disease, amyloidosis) * 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) * Documented room air oxygen saturation reading \< 90% at screening * Planned septal reduction treatment that cannot be deferred during the trial period * History of septal reduction therapy (surgical myectomy or alcohol septal ablation) within 6 months of screening * History of paroxysmal or persistent atrial fibrillation or atrial flutter. Atrial flutter treated with radio frequency ablation without recurrence within the last 6 months prior to screening is allowed. * Current or recent (\< 4 weeks) therapy with disopyramide * History of syncope, symptomatic ventricular arrhythmia, or sustained ventricular tachyarrhythmia with exercise within 6 months prior to screening * Has received prior treatment with aficamten or previously intolerant (reduced LVEF requiring permanent drug discontinuation) to mavacamten