Inclusion Criteria:

• Diagnosed with nHCM (hypertrophied and non-dilated left ventricle in absence of systemic or other known cause), with LV wall thickness ≥ 15mm at Screening or ≥ 13mm with a positive family history of HCM.
• Age 18 and greater, Body weight ≥ 45kg.
• Documented LVEF ≥ 55% at the Screening as determined by echo central lab.
• LVOT gradient < 30 mmHg at rest AND during Valsalva AND post-exercise.
• NYHA functional class II or III.
• Elevated NT-proBNP at rest.

Exclusion Criteria:

• History of syncope, sustained ventricular tachyarrhythmia with exercise, obstructive coronary artery disease or myocardial infarction within the past 6 months.
• History of resuscitated sudden cardiac arrest at any time or known appropriate implantable cardioverter defibrillator (ICD) discharge within 6 months prior to Screening.
• Current treatment with disopyramide or ranolazine (within 14 days prior to Screening).
• Current or planned treatment during the study with a combination of beta-blockers and calcium channel blockers.
• Has been treated with invasive septal reduction (surgical myectomy or percutaneous alcohol septal ablation [ASA]) within 6 months prior to Screening.
• History of resting or post-exercise LVOT >30 mmHg unless subsequently treated by septal reduction.
• Has QTc Fridericia (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 persistent or permanent atrial fibrillation not on anticoagulation for at least 4 weeks prior to Screening and/or not adequately rate-controlled within 1 year of Screening.
• History of clinically significant malignant disease within 10 years such as non-metastatic cutaneous squamous cell or basal cell carcinoma.
• History or evidence of any other clinically significant disorder, condition, or disease that, in the opinion of the investigator or MyoKardia physician, would pose a risk to subject safety or interfere with the study evaluation, procedures, or completion.