African-Americans have bigger hearts than their white peers, according to a large new study by researchers from the University of Texas Southwestern Medical Center. But bigger isn't better, and doctors say enlarged hearts put black people at higher risk for heart disease.

As part of the ongoing Dallas Heart Study, which began in 1999, doctors used cardiac MRI to measure heart mass in 1,335 black and 858 white participants aged 30 to 67. The study, published online by the journal Hypertension, found that blacks were two to three times more likely than whites to have a troublesome enlargement of the left ventricle, a condition called left-ventricular hypertrophy, or LVH. According to the study, LVH is associated with cardiac problems including heart attack, stroke and heart failure.

The study also suggests that LVH in African-Americans is most likely linked to high blood pressure, but not to body fat or general body composition, as doctors had previously suspected. High blood pressure forces the heart to pump harder to distribute blood throughout the body. As a result, the muscle fibers of the heart’s left pumping chamber become thicker, stiffer and less efficient, increasing the chances of congestive heart failure. The study’s authors expressed the hope that their results would spur better cardiovascular screening and more preventative measures in the African-American community.

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