The efficacy and safety of warfarin, aspirin, and the two combined are compared in a long-term, randomized, open, multicentre study involving 3606 patients after acute myocardial infarction (1202 in each treatment group). In this trial three groups receive either warfarin, aimed at a therapeutic level of the International Normalized Ratio (INR) 2.8-4.2, or 160 mg aspirin daily, or 75 mg aspirin daily combined with warfarin with INR 2.0-2.5. A placebo group is not included. Patients are screened before randomization and are given major examinations at 4 weeks and at the end of the study. In addition, all patients are given a questionnaire every 6 months. Composite endpoints include death, non-fatal reinfarction and cerebral stroke. All analyses are conducted on the intention-to-treat principle and on on-efficacy basis. The analyses control for recruiting centre, use of beta blockade, use of thrombolytic therapy and use of angiotensin converting enzyme (ACE) inhibitors.