• Signed informed consent form (ICF): Participants, or their legally acceptable representative, must have signed and dated an Institutional Review Board (IRB)/Independent Ethics Committee (IEC)-approved ICF in accordance with regulatory, local, and institutional guidelines. This must be obtained before the performance of any protocol-related procedures.

• Diagnosed with obstructive hypertrophic cardiomyopathy (HOCM) consistent with Japanese Circulation Society guidelines (2025), i.e., satisfy all criteria below:

  • Has unexplained left ventricular (LV) hypertrophy with nondilated ventricular chambers in the absence of other cardiac (e.g., hypertension, aortic stenosis) or systemic disease and with maximal LV wall thickness ≥ 15 mm (or ≥ 13 mm with positive family history of HCM).
  • Has Left Ventricular Outflow Tract (LVOT) peak gradient ≥ 30 mmHg (resting, Valsalva maneuver, or post-exercise).

• Has documented Left Ventricular Ejection Fraction (LVEF) ≥ 55% at baseline.

• Participants who meet any of the following criteria:

  • Participants who have previously received mavacamten continuously for ≥ 16 weeks
  • Participants who are currently receiving mavacamten
  • Participants who are scheduled to receive mavacamten

• Treated with a stable dose of cibenzoline for at least 3 months prior to initiating mavacamten treatment. Tapered cibenzoline within 3 months prior to initiating mavacamten treatment is allowed if stable dose of cibenzoline was used for at least 3 months prior to tapering.

• At least 18 years of age at the time of signing the informed consent.

• Hypersensitivity to the active substance or to any of the excipients.
• During pregnancy and in women of childbearing potential.
• Treated with strong CYP3A4 inhibitors (itraconazole, clarithromycin, voriconazole, posaconazole, ritonavir, cobicistat, ceritinib, ensitrelvir fumaric acid, lonafarnib, josamycin, or mifepristone/misoprostol).
• Severe hepatic impairment (Child-Pugh C).
• Severe atrioventricular block or severe sinoatrial block.
• Congestive heart failure.
• Requiring dialysis.
• Angle-closure glaucoma.
• Tendency to urinary retention.
• Treated with vardenafil hydrochloride hydrate, moxifloxacin hydrochloride, lascufloxacin hydrochloride (injection), toremifene citrate, fingolimod hydrochloride, siponimod fumarate, or eliglustat tartrate.
• Mavacamten treatment within 8 weeks prior to baseline. Mavacamten treatment initiation was judged based on post-exercise LVOT peak gradient.