"We learn from the medics. They tell us who had a cardiac arrest, and then we go back to the time that they were born, and we get their entire records," Chugh said. When possible, the researchers talked to survivors as well.
Of the 4,557 sudden cardiac arrests identified during the study period, the researchers classified all those that occurred during or within an hour of sex as related to the act itself: 34 cases, or 0.7%. Of these, 32 were men.
Among men then, 1% of the total cardiac arrest cases were triggered by sex, while for women it was 0.1%.
The age range of the patients who suffered arrest during sex was 34 to 83. Heart problems and medications were common among the group. Only a third received cardiopulmonary resuscitation.
"If this devastating event does occur, the partner should not hesitate to perform CPR since it will potentially increase the chances of survival," Chugh said.
Overall, the question of whether having sex might be dangerous to heart patients is one that "needed to be answered," said Dr. Michael J. Ackerman, a professor of medicine, pediatrics and pharmacology at the Mayo Clinic who was not involved in the study. "And it's a wonderful answer for those who love sex."
Heart patients often wonder what activities they can safely resume after a cardiac event. They always ask about exercise and how active they can become," Ackerman said. "They almost never ask directly about sex, but they're always wondering about that." Bring up the topic, and "the floodgates open."
The anxiety is often tremendous, especially for the partner, he said. "They're picturing the fatal event is going to happen if he becomes active again sexually."
Three years ago, Ackerman published a similar study that looked at genetic heart disease patients. He and his colleagues showed that when the genetic condition is diagnosed and treated, sex seldom triggers a cardiac arrest.
"I think it's important to healthy relationships to have this anxiety lifted," he said.
Chugh has expanded his study to include the 850,000 residents of Ventura County, California. The focus there is to identify better ways of predicting and preventing sudden cardiac arrest in Latinos, an understudied group, he said.
"In the big picture, it is rare for sexual intercourse to be a trigger for sudden cardiac arrest," he said.