Mavacamtenis a novel, small molecule, selective allosteric inhibitor of cardiac-specific myosin, for the treatment of patients with symptomatic oHCM. This study will assess the efficacy and safety of mavacamten in Chinese adults with symptomatic oHCM.

This is a randomized, double-blinded, placebo-controlled clinical study witha long-term extension to evaluate the efficacy and safety of mavacamten in Chinese adults with symptomatic oHCM. Approximately 81eligible participants will be enrolled and randomized in a 2:1 ratio (mavacamten:placebo). Participants will receive mavacamten or matching placebofor 30 weeks indouble-blinded manner. After 30-week double-blinded placebo-controlled treatment, eligible participants will receive mavacamten for additional 48 weeks (placebogroup: switch from placebo to mavacamten, mavacamten group: maintain on mavacamten).

Inclusion Criteria:

• Is at least 18 years old at screening.
• Body weight is greater than 45 kg at screening.
• Has adequate acoustic windows to enable accurate TTEs
• Diagnosed with oHCM
• Has documented LVEF ≥ 55% at rest.
• Has a valid measurement of Valsalva LVOT peak gradient at screening
• Has NYHA Class II or III symptoms at screening
• Female participants must not be pregnant or lactating
• Able to understand and comply with the study procedures, understand the risks involved in the study, and provide written informed consent according to national, local, and institutional guidelines before the first study specific procedure.

Exclusion Criteria:

• Participated in a clinical trial in which the participant received any investigational drug (or is currently using an investigational device) within 30 days prior to screening, or at least 5 times the respective elimination half-life (if known), whichever is longer.
• Causing cardiac hypertrophy in other reasons
• Previously participated in a clinical study with mavacamten.
• Hypersensitivity to any of the components of the mavacamten formulation.
• Current treatment (within 14 days prior to screening) or planned treatment during the double-blinded treatment with a combination of beta-blockers and verapamil or a combination of beta-blockers and diltiazem.
• Has been successfully treated with invasive septal reduction
• Has documented obstructive coronary artery disease
• Has known moderate or severe (as per investigator's judgment) aortic valve stenosis, constrictive pericarditis, or clinically significant congenital heart disease at screening.
• Has any acute or serious comorbid condition 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 malignant disease within 10 years of screening
• Has safety laboratory parameters outside normal limits at screening as assessed by the local laboratory
• Has a positive serologic test at screening for infection with human immunodeficiency virus, hepatitis C virus, or hepatitis B virus surface antigen.
• Known uncured COVID-19 (coronavirus disease 2019) infection or with severe complication before screening.
• 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.
• Prior treatment with cardio toxic agents.
• Unable to comply with the study requirements, including the number of required visits to the clinical site.
• Is a first degree relative of personnel directly affiliated with the study at the clinical study site, any study vendor, or the study sponsor.
• Identified as alcohol addicts.

Adverse events were assessed from the first dose date of study medication up to 30 weeks.

Consistent with clinicaltrials.gov definitions.