This is an open-label extension study of China cohort in the phase 3 study (CY 6031) of aficamten for the treatment of obstructive HCM (oHCM) to collect long-term safety and tolerability data, including assessments of cardiac function and steady-state Pharmacokinetics (PK) during chronic dosing with aficamten.

Inclusion Criteria:

1. Completion of a Cytokinetics trial investigating CK-3773274
2. LVEF ≥55% at the Screening Visit

Exclusion Criteria:

1. Has participated in another investigational device or drug study or received an investigational device or drug <1 month (or 5 half-lives for drugs, whichever is longer) prior to screening. Other investigational procedures while participating in this study are not permitted.
2. Since completion of a previous study of aficamten has:Developed new-onset paroxysmal or permanent atrial fibrillation (AF) requiring rhythm restoring treatment (e.g., direct-current cardioversion, ablation procedure, or antiarrhythmic therapy) <30 days prior to screening. Patient may rescreen for JX01003 after 30 days if heart rate (HR) <100 bpm and/or rhythm is stable >30 days.
3. Undergone septal reduction therapy (surgical myectomy or transcatheter alcohol ablation).
4. Had a confirmed LVEF <40% with an associated dose interruption during participation in a prior study with aficamten.
5. History of appropriate implantable cardioverter defibrillator (ICD) shock within 30 days prior to screening.
6. Has received treatment with mavacamten.