Sudden cardiac arrest is associated with sexual activity far more often in men than women, research suggests.
But sex is a rare trigger for sudden cardiac arrest.
Only 34 out of the 4,557 cardiac arrests examined occurred during or within one hour of sexual intercourse and 32 of those affected were men.
Sumeet Chugh, of the Cedars-Sinai Heart Institute, said his study is the first to evaluate sexual activity as a potential trigger of cardiac arrest.
The research was presented at a meeting of the American Heart Association.
A cardiac arrest happens when the heart malfunctions and suddenly stops beating. It causes someone to fall unconscious and stop breathing and unless treated with CPR, it is fatal.
This differs from a heart attack, where blood flow to the heart is blocked.
It is known that sexual activity can trigger heart attacks, but the link with cardiac arrest was previously unknown.
Source: American Heart Association
Dr Chugh and his colleagues in California examined hospital records on cases of cardiac arrest in adults between 2002 and 2015 in Portland, Oregon.
Sexual activity was associated in fewer than 1% of the cases. The vast majority were male and were more likely to be middle-aged, African-American and have a history of cardiovascular disease.
The study also found CPR was performed in only one-third of the cases, despite them being witnessed by a partner.
Dr Chugh said: "These findings highlight the importance of continued efforts to educate the public on the importance of bystander CPR for sudden cardiac arrest, irrespective of the circumstance."
He said it shows the need for people to be educated about how to administer CPR.
Another study presented at the conference showed children as young as six can learn it.
After a heart attack or surgery, the British Heart Foundation suggests patients should typically wait four to six weeks before resuming sexual activity.