Researchers say they’ve uncovered more troubling evidence that African Americans suffer more severe heart disease than other races. New findings published in the journal Circulation show blacks are twice as likely as whites to die from sudden cardiac arrest—and they’re dying younger from the condition, too, NBC News reports.

Sudden cardiac arrest is, simply put, when the heart stops beating. It often happens as a result of a heart attack, but can also be caused by an irregular heartbeat or electrical disturbances. Doctors say the condition is usually fatal, with fewer than 6 percent of people surviving if they experience it outside of a hospital.

For the study, researchers at Cedars-Sinai Heart Institute in Oregon looked at the clinical outcomes of more than 100 African Americans and 1,200 whites from the Portland area who suffered cardiac arrest. They found that black people’s death rates were twice as high as their white counterparts and that they were also, on average, six years younger than whites when it happened.

Researchers said African Americans who died were also more likely to have other diseases, such as diabetes, high blood pressure and kidney disease. But the study noted that this group’s higher burden of illness could only be partly to blame for the racial differences in survival rates.

“These findings suggest the possibility that when it comes to the prevention of sudden cardiac death, different races and ethnicities may not necessarily be painted with one broad brush,” said Sumeet Chugh, MD, of Cedars-Sinai, a senior author on the study.

Click here to learn one possible reason why African Americans are more likely to die after cardiac arrest.