Much of cardiovascular disease can be treated on the basis of the results of large clinical trials and can be considered 'evidence-based'. However, trial results are not infallible and it is important to recognize their limitations. Despite the evidence, widespread variation exists in medical practice between and within countries; the reasons may be cultural, or may indicate poor medical education. Purchasing authorities have to do the best they can with available evidence, and our full evidence base needs to include costs; in some instances we now have evidence of benefit from treatment that we almost certainly cannot afford. Evidence-based medicine is a further - but possibly an acceptable - limitation to clinical freedom.