A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether prophylactic haemofiltration during cardiopulmonary bypass is of benefit during cardiac surgery? Altogether 273 papers were found using the reported search, of which nine presented 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 of these papers are tabulated. We conclude that haemofiltration will increase the haematocrit, reduce some inflammatory markers and may increase the variability of heparin levels. It may also reduce post-operative blood transfusion and possibly increase BP and cardiac index immediately after haemofiltration, although no differences in morbidity or mortality has ever been shown.