A follow-Up, Open-Label, Research Evaluation of Sustained Treatment with Aficamten (CK-3773274) in Hypertrophic Cardiomyopathy (HCM)

FOREST HCM (CY 6022) is an open-label extension designed to assess the long-safety and tolerability of chronic dosing with Aficamten in participants with HCM who have been taking HCM medications. The study aims to determine the dose level of Aficamten that is best tolerated and because of this, dosing of the drug may be increased or decreased as needed.

This is an open-label study, which means the participant and the study team will know the dose of Aficamten and begin at the lowest dose of 5 mg per day and increased over time at the discretion of the study doctor by titration. The maximum dose is 20 mg per day taken by mouth once daily in a tablet form.

The study involves a screening period of up to 56 days and completion of a Cytokinetics study investigating Aficamten within 6 months of screening. If the screening results show eligible to continue in the study, visits will be on Day 1 for first dosing day, then every 4 weeks for the first 24 weeks. Thereafter, clinic visits can occur every 6-12 months under approval of the study doctor and dosing for approximately 5 years.

During these visits:

• scheduled echocardiograms
• blood collections
• electrocardiograms
• vital signs
• physical examinations will be conducted.

Optional Cardiac Magnetic Resonance (CMR) imaging sub-study, also referred to as cardiac MRI, sub-study by signing the separate CMR sub-study consent form, they will undergo a cardiac MRI anytime during the screening period and at other scheduled visits until the end of treatment.