Open-label Extension Study to Evaluate the Long-term Safety and Tolerability of Aficamten in Adults With HCM

Inclusion Criteria:

• Completion of a Cytokinetics trial investigating aficamten

• LVEF ≥ 55% at the Screening Visit

Exclusion Criteria:

• Has received treatment with mavacamten: (a) within 56 days prior to dosing and (b)has not received approval for participation from the Medical Monitor.

• Has participated in another investigational device or drug study or received aninvestigational device or drug < 1 month (or 5 half-lives for drugs, whichever islonger) prior to screening. Other investigational procedures while participating inthis study are not permitted.

• Since completion of a previous trial of aficamten has:

• Developed new-onset paroxysmal or permanent atrial fibrillation requiringrhythm restoring treatment (eg, direct-current cardioversion, ablationprocedure, or antiarrhythmic therapy) < 30 days prior to screening. Patient mayre-screen for CY 6022 after 30 days if heart rate (HR) < 100 bpm and/or rhythmis stable > 30 days

• Undergone septal reduction therapy (surgical myectomy or transcatheter alcoholablation)

• Had a confirmed LVEF < 40% with an associated dose interruption during participationin a prior study with aficamten

• History of implantable ICD placement within 30 days prior to screening.