Some of the indications for anticoagulant therapy remain controversial, but they are widely used for the prevention and treatment of thrombosis and embolism after surgery1 and after myocardial infarction,2 in patients with atrial fibrillation, and in those with transient cerebral ischaemia.3 This article discusses the drugs available for long-term use. Those suitable for immediate and short-term use, heparin and arvin, will be discussed in the next issue.