Extension Study of Mavacamten (MYK-461) in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy Previously Enrolled in PIONEER

Key Inclusion Criteria:

- Completed Study MYK-461-004

- Body weight > 45 kg

- Has safety laboratory parameters (chemistry and hematology) within normal limits

Key Exclusion Criteria:

- Has QTcF > 480 ms or any other ECG abnormality considered by the investigator to pose
a risk to subject safety (eg, second degree atrioventricular block type II)

- Since enrollment into Study MYK-461-004, has developed obstructive coronary artery
disease (> 70% stenosis in one or more arteries) or known moderate or severe aortic
valve stenosis

- Since enrollment into Study MYK-461-004, has developed any acute or serious comorbid
condition (eg, major infection or hematologic, renal, metabolic, gastrointestinal, or
endocrine dysfunction) that, in the opinion of the investigator or medical monitor,
would pose a risk to subject safety or interfere with the study evaluation,
procedures, or completion

- Since enrollment into Study MYK-461-004 has developed clinically significant malignant
disease