During the month before and after childbirth, African-American women are at a significantly higher risk than white women for developing peripartum cardiomyopathy (PC), a condition that causes an enlarged stiff heart muscle that no longer pumps efficiently, according to study findings from the Medical College of Georgia (MCG), published in the Journal of the American College of Cardiology.

PC typically occurs in the last month of pregnancy or a few months after delivery.

For the study, researchers examined PC incidence among women who gave birth in a five-year period at MCG's teaching hospital. Scientists found that although 55 percent of the women were white, 93 percent of mothers who developed PC were black.

“When it hits, it's totally unexpected because these are young, otherwise healthy women with young children,” said Mindy B. Gentry, MD, an MCG cardiologist and a study author. “[They aren't patients] you'd expect to have any sort of health problem—much less heart failure.”

Two previous PC studies (with all black participants), one in Haiti and the other in South Africa, showed a higher incidence of the condition in these countries as compared with other parts of the world.

The mixed population giving birth at MCG's hospital made it easier for researchers to assess the effect of race, Gentry noted.

Scientists don't know why the condition occurs more often among black women, but they're looking for environmental and genetic factors that might explain the heightened risk.

In addition, researchers have started studying racial differences in healthy women's hearts during childbirth.

Although drugs can improve the heart's pumping ability, PC is a potentially life-threatening and debilitating condition. PC mortality rates range from 15 to 56 percent.

Read how breast feeding could protect your heart here.