Given the rapid evolution of cardiovascular medicine, clinicians must sift through an enormous array of information about new therapies in order to determine how best to treat patients with ischemic heart disease. They should first consider the evidence from randomized clinical trials, because these trials eliminate bias and permit broad statistical analyses. If randomized clinical trial data are not available, next in order of the strength of their evidence are observational studies, historically controlled studies, case series, and case reports. Clinicians must additionally ascertain that an investigation has the elements of good design, including a clear question, adequate sample size, appropriate inclusion and exclusion criteria, evidence that the right amount of data was collected carefully, and allowances in the analyses for patients taking multiple therapies and randomized into several clinical trials.