A subtle, unexpected attack on the coronary arteries by the body's own immune system may be the cause of as many as half of all of heart attacks and cases of coronary artery disease, Harvard scientists report today.

If the study is confirmed, it suggests that pharmaceutical companies should explore development of a whole new class of heart drugs that focus on inflammation, the researchers said. It also suggests that a high risk of heart attack in at least some patients could be detected with a simple blood test as long as eight years in advance of a potential heart attack.

Researchers have been interested in the role of infectious agents and inflammation in heart disease because the conventional risk factors--smoking, hypertension, high cholesterol levels--explain only about half of all heart attacks. The other half "is a substantial unknown territory," said Dr. George Sopko of the National Heart, Lung and Blood Institute.