The spectrum of acute coronary syndromes (ACS) includes several clinical complexes that frequently cause critical instability in affected patients. This article focuses on several critical care aspects of these unstable ACS patients. The management of cardiogenic shock can be particularly challenging because the mechanical defects are varied in cause, severity, and specific treatment. Complications of fibrinolytic therapy are potentially deadly and arrhythmias are relatively common in the ACS patients. Discussions on the management of these problems should help the emergency physician more effectively to treat critically ill patients with ACS.