Heparin and antiaggregating therapy represent an effective treatment of unstable angina. Aspirin is able to prevent myocardial infarction and death in patients with unstable angina, but is not able to control myocardial ischemia. On the contrary, heparin administered by continuous intravenous infusion (about 1,000 U/h) controls myocardial ischemia by very early lowering anginal attacks and silent ischemic episodes. Heparin intermittently administered (6,000 U i.v. four times daily) did not significantly affect anginal attacks and myocardial ischemia. Thrombolytic therapy alone (Alteplase 1.75 mg/kg) reduced, but not significantly, the number of anginal attacks. The reduction of myocardial ischemia induced by continuous infusion of heparin is associated with a decrease of fibrinopeptide A plasma levels, whereas the thromboxane B2 production by platelets seems to be irrelevant in order to obtain a reduction of myocardial ischemia. Thus thrombin formation seems to be a primary factor in the occurrence of refractory unstable angina and in the activation of platelets.