Harmony Reynolds, a cardiologist at NYU Langone Medical Center, recently led a study that subjected 20 women to a host of tests designed to bring on physical and mental stress.

The study looked for possible reasons some of the women had suffered a mysterious ailment known as broken-heart syndrome, which mimics a heart attack but generally doesn’t appear to be due to coronary artery disease.

In seeking a common thread among the 10 women in the group who had experienced an attack of broken-heart syndrome over the past several years, Dr. Reynolds and colleagues came to suspect they each suffered from an impaired parasympathetic nervous system, the part of the nervous system responsible for helping the body calm down.

The study led to strikingly different conclusions from what other researchers had previously believed might be behind the unusual malady. It also led Dr. Reynolds to believe that breathing and other relaxation techniques such as yoga and meditation should be tested for preventing broken-heart syndrome.

Experts say broken-heart syndrome, which most often affects women in their 60s or older, can be brought on by strong emotions, such as grief, anger and anxiety, or by physical stress. A common trigger is a loved one’s illness or death, while for some patients there is no clear-cut cause for an attack. “It is a romantic notion, but you really can get this from heartache,” says Dr. Reynolds, whose study was published online in November in the American Journal of Cardiology.