March 28 (HealthDay News) -- Higher rates of diabetes and hypertension could be driving the especially high rate of heart failure among American blacks, a new study finds.

The study of 7,000 men and women, ages 45 to 84, found that black Americans developed heart failure at a much higher rate (4.6 per 1,000 people per year) than all other races, including whites (2.4 cases per 1,000 per year) and Chinese Americans (1 case per 1,000 per year).

However, when the Johns Hopkins University team used statistical techniques to exclude diabetes and blood pressure -- two traditional risk factors for heart failure -- these racial differences virtually disappeared.

"When all major factors are taken into account, the difference between races for heart failure largely evaporate in the absence of diabetes and hypertension among African Americans," senior investigator Dr. Joao Lima, associate professor of medicine and radiology at the Johns Hopkins University School of Medicine and its Heart Institute, said in a prepared statement.

Black Americans are nearly twice as likely as whites to be diagnosed with diabetes and more than a third more likely than whites to have high blood pressure, the study authors noted.

The findings send a clear message to doctors that "warding off heart failure in African Americans requires aggressive treatment of diabetes and hypertension," study lead researcher Dr. Hossein Bahrami, a senior cardiology fellow, said in a prepared statement.

"Whether through increased screening or greater emphasis on drug therapies, these are two risk factors that must be brought under control," Bahrami said.

The study was presented Tuesday at the American College of Cardiology meeting, in New Orleans. The same study found race-based differences in the heart's rhythm, with black Americans' hearts contracting at a slightly weaker rate than that of whites or Chinese Americans.