Doctors said it was one of the best tests of specific diets on heart health, especially because dieters stuck to it and achieved the goals for various fats that researchers set. The participants also were similar in treatments and other factors so the effect of the diets could be isolated.

"Both diets are prudent choices" for people at high risk of heart disease, said study leader Dr. Katherine Tuttle of Providence Medical Research Center in Spokane, Wash. She presented the results at the conference.

Both the Heart Association diet and the Mediterranean diet are low in saturated fat (less than 7 percent of total calories) and cholesterol (less than 200 milligrams a day). The typical American's diet contains twice those levels or more, Tuttle said.

Those on the American Heart diet were told to keep total fat intake to less than 30 percent of calories. The Mediterranean dieters were allowed to go up to 40 percent, with the extra coming from foods containing healthy fats, such as fish, avocados and olive oil.

Researchers thought this diet would prove best, because of the heart-helpful omega-3 fatty acids in the fish.

They tested this hunch on 202 people who had suffered heart attacks in the previous six weeks. Fifty were put on the low-fat diet and 51 on the Mediterranean diet. Both groups received two individual diet counseling sessions in the first month and six group sessions over the next two years.

The other 101 served as a comparison group. "They got the usual advice," Tuttle said.

All were prescribed standard drugs like aspirin, beta blockers and statins to lower cholesterol. Deaths, second heart attacks, strokes and heart-related hospitalizations were tracked.

After four years, 83 percent of those on the low-fat or Mediterranean diets had survived without such problems; 53 percent of the others did. Cholesterol levels improved in both diet groups but not the comparison group.