A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether addition of anti-platelet therapy to warfarin reduced the incidence of thromboembolic complications in patients with prosthetic heart valves. Altogether 253 papers were found using the reported search, of which 11 papers represented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses were tabulated. We conclude that low dose aspirin (80-100 mg daily) in addition to warfarin in patients with prosthetic heart valves reduces all cause long term mortality (NNT=19), with significant reductions in thromboembolism but an increase in bleeding.