This clinical trial enrolled 1,587 patients in 142 medical centers; VA and non-VA centers in the U.S., and medical centers in the United Kingdom and Canada. Patients were randomly and equally allocated to the 3 treatments: warfarin (administered open-label), aspirin and clopidogrel (the latter two administered double-blind). The study was conducted over a 3.5 year period, with a 2.5 year enrollment phase.