First-in-class drug brightens outlook for those diagnosed with hypertrophic cardiomyopathy in childhood
NEW ORLEANS (March 29, 2026) — Adolescent patients with obstructive hypertrophic cardiomyopathy (HCM) who received the drug mavacamten saw a significant improvement in left ventricular outflow tract (LVOT) gradient, a measure of blood flow obstruction in the heart, compared with those who received a placebo, according to a small study presented at the American College of Cardiology’s Annual Scientific Session (ACC.26). The trial is the first to test mavacamten in patients younger than 18.
“These results are very encouraging,” said Joseph William Rossano, MD, chief of cardiology at Children’s Hospital of Philadelphia and the study’s lead author. “Patients feel better, and their hearts look better.”
HCM is a genetic disorder in which the heart muscle thickens, causing the heart chambers to become smaller and potentially reducing its ability to pump blood. In many cases, the thickened muscle blocks or reduces the flow of blood into the aorta from the left ventricle, known as obstructive HCM. Obstructive HCM can cause symptoms such as chest pain, dizziness, shortness of breath and swelling and lead to heart failure and death.
While the disorder can go undetected for decades, patients diagnosed with obstructive HCM during childhood tend to have more severe forms of the disease, with heart failure and the need for a mechanical pump or heart transplant being more common when the disease is diagnosed in childhood. At the same time, available medications used to treat HCM in adults are often less effective or less safe for children.
Mavacamten is a first-in-class drug that reduces the heart’s squeezing strength by inhibiting myosin, a protein involved in muscle contraction. It is currently approved by the U.S. Food and Drug Administration for adults with obstructive HCM.
“This medicine was specifically designed for HCM and treats the underlying pathophysiology. This is what we hope to do in health care—to get medicines that are targeted for the underlying problem,” Rossano said.
The trial enrolled 44 patients with obstructive HCM between the ages of 12-17 years in North America, Europe and Australia. Participants had activity-limiting heart failure symptoms, peak LVOT gradients >50 mmHg and normal left ventricular ejection fraction (above 60%). Half of the participants were randomly assigned to receive mavacamten and half took a placebo daily for 28 weeks.
Participants receiving mavacamten saw a substantial improvement in terms of the study’s primary endpoint, change in Valsalva LVOT gradient from baseline to week 28, with an average drop of 48.5 mmHg in this group compared with a drop of 0.5 mmHg among those taking placebo. Secondary endpoints including change in resting LVOT gradient, maximal left ventricular wall thickness, peak oxygen consumption, and measures of symptoms such as fatigue and shortness of breath were also significantly improved in favor of mavacamten.
In addition, levels of troponins and peptides—markers of heart damage—decreased in those taking mavacamten and increased in those taking placebo. This suggests that taking mavacamten could not only help slow disease progression but actually reverse some of the damage it causes, Rossano said.
“Beyond symptom relief, there’s a signal that this may be favorably remodeling the heart, which could improve the natural history of the disease,” he said. “This suggests that it could be important to start children on this therapy when they’re young, before they’ve had many decades of ongoing injury to the heart from the obstruction. However, longer term follow-up is needed to confirm these findings.”
The results, which were similar to previous clinical trials conducted in adults with HCM, did not point to any safety concerns, with comparable rates of adverse events seen in both study arms and no significant reduction in ejection fraction, a measure of the heart’s pumping ability.
The study was limited by its relatively small size, short duration and predominately White population. The researchers plan to continue tracking outcomes to at least 50 weeks. Rossano said that future studies could investigate the drug’s efficacy in children younger than 12 years old and in people with different types of HCM.
The study was funded by Bristol Myers Squibb, maker of mavacamten.
This study was simultaneously published online in the New England Journal of Medicine at the time of presentation.
Rossano will present the study, “Mavacamten in Symptomatic Adolescent Patients with Obstructive Hypertrophic Cardiomyopathy: Results from the Phase 3 Scout-HCM Trial,” on Sunday, March 29, at 10:45 a.m. CT / 15:45 UTC in the Main Tent, Great Hall.
ACC.26 will take place March 28-30, 2026, in New Orleans, bringing together cardiologists and cardiovascular specialists from around the world to share the newest discoveries in treatment and prevention. Follow @ACCinTouch, @ACCMediaCenter and #ACC26 for the latest news from the meeting.
The American College of Cardiology (ACC) is the global leader in transforming cardiovascular care and improving heart health for all. As the preeminent source of professional medical education for the entire cardiovascular care team since 1949, ACC credentials cardiovascular professionals in over 140 countries who meet stringent qualifications and leads in the formation of health policy, standards and guidelines. Through its world-renowned family of JACC Journals, NCDR registries, ACC Accreditation Services, global network of Member Sections, CardioSmart.org patient resources and more, the College is committed to ensuring a world where science, knowledge and innovation optimize patient care and outcomes. Learn more at ACC.org.
###