A Long-Term Safety Extension Study of Mavacamten in Adults Who Have Completed MAVERICK-HCM or EXPLORER-HCM

Key Inclusion Criteria:

- Has completed MAVERICK-HCM through Week 24 within the past 3 months

- Has a body weight greater than 45 kg

- Has adequate acoustic windows to enable accurate echocardiograms.

- Female participants must not be pregnant or lactating and, if sexually active, must be
using acceptable birth control methods from the Screening visit through 3 months after
the last dose of investigational medicinal product (IMP).

- Male participants with sexual partners must agree to use condoms for the duration of
the study and for 3 months after the last dose of study drug in order to prevent
passing mavacamten to the partner in the ejaculate

- Has documented LVEF ≥ 55% by echocardiography core laboratory

- Has safety laboratory parameters (chemistry, hematology, coagulation, and urinalysis)
within normal limits (according to the central laboratory reference range).

Key Exclusion Criteria:

- Has a history of syncope or a history of sustained ventricular tachyarrhythmia with
exercise within the past 6 months

- Has a history of resuscitated sudden cardiac arrest or known history of appropriate
implantable cardioverter-defibrillator (ICD) discharge for life-threatening
ventricular arrhythmia within the past 6 months

- Currently treated with disopyramide or ranolazine (within 14 days prior to Screening)
or treatment with disopyramide or ranolazine is planned during the study

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

- Has any acute or serious comorbid condition (eg, major infection or hematologic,
renal, metabolic, gastrointestinal, or endocrine dysfunction) that, in the judgment of
the investigator, could lead to premature termination of study participation or
interfere with the measurement or interpretation of the efficacy and safety
assessments in the study

- History of clinically significant malignant disease that developed since enrollment in
MAVERICK-HCM

- Has a history or evidence of any other clinically significant disorder, condition, or
disease that, in the opinion of the investigator, would pose a risk to participant
safety or interfere with the study evaluation, procedures, or completion

- Is unable to comply with the study requirements, including the number of required
visits to the clinical site