The clinical consequence of thrombosis, superimposed upon ruptured or eroded plaque in coronary arteries, is an acute coronary syndrome. The clinical manifestations are dependent upon the extent of obstruction to perfusion, microembolization, and the volume of muscle affected. Even in the absence of complete occlusion, about 8% to 13% of patients die within 6 months. Antiplatelet and antithrombin therapies have been tested in large-scale clinical trials with consistent and robust findings. In addition to the benefits of aspirin, thienopyridines and intravenous glycoprotein IIb/IIIa inhibitors improve outcome. Combined antithrombin and antiplatelet treatment is more effective than either alone. Unfractionated and low-molecular-weight heparins reduce cardiac events, but direct antithrombins (hirudin) have not shown convincing clinical benefit. Novel preparations are in development, and show promising results...