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April 14 (Reuters) - Bristol Myers Squibb's BMY.N drug to treat a type of heart disease did not significantly improve functional capacity and symptoms in patients, failing to meet the main goals of a late-stage study, the company said on Monday.

The New Jersey-based company's shares fell 1.6% in extended trading.

The drug, mavacamten, was tested in adult patients with non-obstructive form of hypertrophic cardiomyopathy (nHCM), an inherited condition characterized by thickening of heart muscles.

HCM affects about one in five adults worldwide and is the most common identifiable cause of sudden cardiac death in healthy young people in the United States, according to government data.

The drug, branded as Camzyos, is already approved in the U.S. for the larger, obstructive form of the disease, which could block blood flow out of the heart.

The trial failure is reflective of the difficulty showing benefit in less severe patient populations, BMO Capital Markets analyst Evan Seigerman said, adding that it mounts "pressure on subsequent catalysts that need to be positive to shift the BMY story."

The drugmaker said no new safety signals were observed in the study.

The label for Camzyos contains a boxed warning, the FDA's strictest, for the risk of heart failure.

The study, which enrolled 580 patients with symptomatic nHCM, used a patient-reported clinical questionnaire to assess their health status, including frequency of symptoms, physical and social limitations.

Mavacamten also failed to improve patients' exercise capacity in the study as measured by peak oxygen consumption after 48 weeks of treatment.

The company said it plans to share detailed trial results with the scientific community in the future.

(Reporting by Mariam Sunny in Bengaluru; Editing by Alan Barona)

((Mariam.ESunny@thomsonreuters.com))