In the 10 years since our previous review of this topic, the acute coronary syndromes (Q wave myocardial infarction [QMI], non-Q wave MI [NQMI], and unstable angina) have been more clearly categorized. Many of the differences delineated between QMI and NQMI still hold: a less extensive infarction and a lower in-hospital mortality, but a larger degree of jeopardized myocardium leading to a higher incidence of reinfarction and recurrent angina. The pathophysiology of NQMI appears to be similar to that of unstable angina except for the greater incidence and extent of thrombus formation and coronary artery occlusion with NQMI. Prognostic studies have shown that ST depression and anterior infarct location are associated with a greater risk for posthospital clinical events than the findings of ST elevation and other infarct locations. Symptom-limited stress testing using electrocardiogram and thallium-201 imaging are now recommended before discharge or in the early postdischarge period, with coronary arteriography recommended for evidence of residual ischemia. Aspirin and low dose heparin should be administered on admission after NQMI to decrease further thrombus formation, and aspirin continued in the posthospital period. Diltiazem administration is recommended in NQMI without evidence of pulmonary congestion to prevent recurrent nonfatal acute myocardial infarction. Percutaneous transluminal coronary angioplasty and surgical revascularization should be reserved for patients with NQMI with residual ischemia.