The enlarged organ tugs apart the mitral valve, which controls blood flow from the left atrium into the left ventricle. The distorted valve functions poorly, its flaps swinging apart. Blood that is supposed to be pumped into the body backs up into the heart and lungs.

A vicious cycle ensues: The heart enlarges, so the mitral valve leaks. The leaky mitral valve makes the heart enlarge even more, as it tries to compensate, and heart failure worsens.

In the new study, a device called the MitraClip was used to repair the mitral valve by clipping its two flaps together in the middle. (The clip is made by Abbott, which funded the study; outside experts reviewed the trial data.)

The result was to convert a valve that barely functioned into one able to regulate blood flow in and out of the heart.

Until today, researchers were not sure that fixing the mitral valve would do much to help these patients. A smaller study in France with similar patients failed to find a benefit for the MitraClip.

But that research included many patients with less severe valve problems, the procedure was not performed as adeptly, and the patients’ medications were not as well optimized as in the new study.

In the new trial, 614 patients with severe heart failure in the United States and Canada were randomly assigned to receive a MitraClip along with standard medical treatment or to continue with standard care alone.