The warnings come from Italian researchers who reviewed previous studies on the causes of infidelity and its effects.
These showed "sudden coital death" to be much more common when a man was meeting his mistress than when he was with his wife.
The researchers could not be sure why but put forward a variety of reasons, including a guilty conscience, the 'Daily Mail' reported.
The review's authors, from the University of Florence, began by scouring medical literature for research papers including the words 'unfaithfulness', 'extramarital affairs', 'infidelity' and 'men'.
This provided information about the type of man who is unfaithful and the potential consequences.
The analysis showed that heart attacks, including fatal ones, were relatively rare when a man was having sex with his wife at home. But when he started to play away, the dangers grew.
German studies show that most men who died during sex were having an affair and meeting away from the family home.
Furred-up arteries were blamed for more than a third of the deaths --the physical demands of sex are said to cause the fatty plaque that has built up inside arteries to rupture.
Liaisons away from home and with younger women are particularly dangerous.
The stress of wining, dining and satisfying a woman who is likely to be younger than the man's wife may also be to blame, as can the strain of keeping an affair secret.
"Extra-marital sex may be hazardous and stressful because the lover is often younger than the primary partner and probably sex occurs more often following excessive drinking or eating," Researcher Dr Alessandra Fisher said.
"It is possible that a secret sexual encounter in an unfamiliar setting may significantly increase blood pressure and heart rate, leading to increased oxygen demand," he said.
"Guilt may also play a role with some research suggesting heart problems are more common among cheats who are still attracted to their wife. Betraying this partner could punish him," Fisher added.
The overview also suggests that in any one year, 4 per cent of married men have an affair. Over the course of a man's life, there is a 50-50 chance of him straying.
