Fondaparinux (Arixtra, GlaxoSmithKline) is a synthetic, selective, activated Factor X inhibitor. On the grounds of its favorable benefit:risk ratio, fondaparinux is approved for the prevention and treatment of venous thromboembolism. Two large trials involving approximately 32,000 patients recently evaluated fondaparinux in the treatment of non-ST elevation acute coronary syndromes and ST elevation acute myocardial infarction. Fondaparinux was compared with enoxaparin or usual care, depending on the setting. A single, once-daily 2.5-mg subcutaneous dose of fondaparinux was used in both studies. After a brief introduction to the drug, this article presents the results obtained in these trials with fondaparinux and compares them with those obtained with other anticoagulants. Overall, it appears that fondaparinux at the single, once-daily dose of 2.5 mg represents a valuable new alternative for the treatment of patients with acute coronary syndromes.