Over half of the cardiovascular-related deaths in the United States are caused by heart attacks. When oxygenated blood cannot flow to an area of the heart muscle, a heart attack may occur. Heart attacks or coronary infarctions can result from a blocking of a blood vessel due to an accumulation of fatty substances on the inside wall of an artery (arteriosclerosis). They are also caused by blood clots which form in the heart (a thrombus), or by clots that form in other areas of the body and circulate to the heart (an embolus).

Many strategies have been developed to prevent the deposits of cholesterol, fibrin (a clotting material), and cellular debris which combine to form a thrombus. Such anticoagulants as aspirin, warfarin, and heparin thin the blood and help to prevent initial clot formation. Until recently, however, very few therapies were able...