The human heart is a muscle, but it’s also a kind of complicated balloon—a balloon that fills and empties roughly 60 to 100 times every minute, and several billion times during the course of a lifetime.

Among people with hypertrophic cardiomyopathy, the walls of the heart muscle are abnormally thick. This thickness can interfere with the heart’s normal filling-and-emptying operation. “If you think of a balloon made with super-thick rubber, you have to blow harder to fill it, and it’s the same with a hypertrophic heart,” says Dr. Daphne Hsu, professor of pediatrics and medicine at Pediatric Heart Center of Montefiore/Einstein in New York. 

Hypertrophic cardiomyopathy is the most common form of genetic heart disease in the U.S. and the second commonest heart-…