Acute coronary syndromes (unstable angina and non-Q-wave myocardial infarction) are caused by the rupture of an atherosclerotic plaque, platelet activation, and fibrin deposition, resulting in thrombosis. Aspirin and unfractionated heparin (UFH) have traditionally been the treatment of choice in patients with acute coronary syndromes. Low-molecular-weight heparins (LMWHs) offer potential advantages over UFH and have been shown to be equally effective as UFH for the treatment and prevention of many venous thromboembolic processes. Results of prospective, randomized, controlled trials evaluating the role of LMWH in the management of patients with unstable angina or non-Q-wave myocardial infarction have indicated improved outcomes when compared with UFH. In addition, despite the increased acquisition cost of LMWH compared with UFH, an overall cost saving was associated with LMWH use, primarily as a result of a reduction in cardiovascular events. The available evidence supports improved clinical outcomes, favorable safety profile, and cost savings associated with LMWH use in the management of unstable angina and non-Q-wave myocardial infarction. Thus, LMWH should replace UFH as the antithrombotic agent of first choice in the management of acute coronary syndromes.