In order that patients receive optimal care, physicians must be able to read and interpret clinical trials critically and to incorporate advances into their treatment regimens. In evaluating clinical trials, not only should results be compared but also the critical issues identified that may influence the outcome of the study. In the clinical trials comparing the low molecular weight heparins (LMWHs) nadroparin, dalteparin, and enoxaparin with unfractionated heparin in the management of patients with unstable angina and non-Q wave myocardial infarction, only the trials of enoxaparin found an unequivocal benefit of LMWH relative to unfractionated heparin. Through an analysis of the trials it is clear that seemingly small differences in design have the potential to have a significant impact on the outcomes of these studies. While obvious aspects such as differences between the drugs under study must be considered, issues such as whether a trial is blind or open, how patients are selected and managed, the relative amounts of medications given, and how end-points are defined all contribute to the outcomes of clinical trials. In this light, it is possible that nadroparin and dalteparin may eventually prove superior to unfractionated heparin in future trials. However, enoxaparin is the only LMWH shown to be more effective than heparin, as demonstrated by both the ESSENCE trial and the more recent TIMI 11B investigation.