Researchers are claiming that pregnancy and hormonal changes that continue 12 weeks after a woman gives birth increase the risk of suffering a heart attack.
Although the risk is very low - 1 in 16,000 births - it is still 3 to 4 times higher than that of non-pregnant females of the same age.
The study, which was presented at the annual scientific sessions of the American College of Cardiology meeting in Chicago this week, also found that heart attacks which occurred during pregnancy were more severe and lead to more complications.
The research team said that hormonal changes, increased blood volume and other physiological changes that happen during pregnancy increased the risk, and that cardiac arrests in pregnant women happen for different reasons to those suffered by other people.
The most common cause in general was atherosclerosis, a narrowing of the arteries, yet in pregnant women, this only accounted for a third of attacks.
The more common reason in pregnancy was coronary dissection, where the layers of the artery wall that blocks blood flow separate - something which is very rare among non-pregnant patients.
The researchers came to the conclusion that this suggests that in at least some cases, the traditional approach to treating coronary dissection in pregnancy and just after birth may not always be the best way.
Dr. Uri Elkayam of the University of Southern California in Los Angeles who led the study told Reuters: "We have very clear guidelines for (heart attack) in the general population. These guidelines, however, may not always apply to women with pregnancy-associated heart attacks and may actually cause more harm than good."
The team looked at 150 cases of heart attacks in pregnant women that occurred since 2005 and found most pregnant women did not have traditional cardiovascular risk factors, like high cholesterol, high blood pressure or diabetes. Despite this, the pregnant women's heart attacks were more severe and the death rates higher.