Mavacamten is the first approved cardiac myosin inhibitor for symptomatic obstructive hypertrophic cardiomyopathy (HOCM), targeting myocardial hypercontractility and reducing left ventricular outflow tract (LVOT) obstruction. While randomized trials have demonstrated its efficacy and safety in adults, data in pediatric patients remain scarce. The ongoing SCOUT-HCM trial is the first phase 3 randomized study evaluating mavacamten in symptomatic adolescents with HOCM. Real-world pediatric experience is currently limited.

We report an initial real-world experience with mavacamten in pediatric patients with HOCM in France. Patients had persistent LVOT obstruction despite maximally tolerated beta-blocker therapy. Clinical and echocardiographic parameters were assessed at baseline and after 3 months of follow-up.

Four pediatric patients aged 15–17 years, all male, with a median weight of 103.4 kg (range: 45–135) were treated. The median duration of prior beta-blocker therapy was 3.5 months. Genetic analysis showed that two patients carried pathogenic variants (MYH7 and MYBPC3), while two patients were genotype-negative. Mavacamten was initiated at 2.5 mg in two patients and 5 mg in two patients, with repeated echocardiographic monitoring. At baseline, the median left ventricular ejection fraction (LVEF) was 65% (range: 64–65). The median LVOT gradient at rest was 23 mmHg (range: 15–100) and with exercise was 79 mmHg (range: 55–110) under maximal beta-blocker therapy.

After 3 months, the median LVOT gradient decreased to 17 mmHg (range: 14–20) at rest and 48.5 mmHg (range: 37–60) with exercise. LVEF remained preserved, with a median of 62% (range: 60–65). Treatment was well tolerated, with no reported adverse events.

In this small real-world pediatric cohort with HOCM, initiation of mavacamten after maximal beta-blocker therapy was feasible and appeared safe at 3-month follow-up. These findings support further evaluation of mavacamten in pediatric patients alongside ongoing clinical trials.