Argatroban is an arginine derivative that is a highly specific thrombin inhibitor. Experimentally, it is more effective than heparin but it is not known whether this is the case in humans. The trials reported with argatroban to date have been too small to define either the efficacy or the safety of the drug. Large-scale clinical trials are under way in a variety of settings, including unstable angina, coronary angioplasty and acute myocardial infarction.