Having, and enjoying, sex in later years can lower the risk of hypertension in women, but may double the risk of heart attacks in men, research shows.
A study by Michigan State University found that older men who had sex once a week or more were twice as likely to have cardiovascular episodes five years later than men who were not sexually active.
But women who participated in the study and who said they found sex to be extremely pleasurable or satisfying were found to be at lower risk of hypertension.
Hui Liu, associate professor of sociology at the university, said: "These findings challenge the widely held assumption that sex brings uniform health benefits to everyone."
The study, which researchers claim is the first large-scale study into how sex affects heart health in later life, surveyed 2,204 people aged 57-85 between 2005-2006, and then again five years later.
Prof Liu said: "Strikingly, we find that having sex once a week or more puts older men at a risk for experiencing cardiovascular events that is almost two times greater than older men who are sexually inactive.
"Moreover, older men who found sex with their partner extremely pleasurable or satisfying had higher risk of cardiovascular events than men who did not feel so."
She said the findings suggest that medical and emotional problems later in life can cause men to exert themselves more in a sexual relationship, leading to exhaustion and stress on the cardiovascular system.
Testosterone levels and the use of medication to improve sexual function may also play a role.
Prof Liu said: "Although scientific evidence is still rare, it is likely that such sexual medication or supplements have negative effects on older men's cardiovascular health."
But commenting on the positive impact of enjoying sex for older women, she said: "Previous studies suggest that strong, deep and close relationship is an important source of social and emotional support, which may reduce stress and promote psychological well-being and, in turn, cardiovascular health.
"This may be more relevant to women than to men, because men in all relationships, regardless of quality, are more likely to receive support from their partner than are women.
"However, only women in good quality relationships may acquire such benefits from their partner."
The findings are published in Journal of Health and Social Behaviour.