Some randomized controlled clinical trials (RCTs) involving antiarrhythmic agents have recently reported unexpected findings. Cardiologists have tried to explain these unforeseen results by pointing to possible inadequacies of trial design. Details of the design and the conduct of RCTs are essential for the proper interpretation of the data that emerge from the trial. Unless an RCT is carefully designed and meticulously conducted, the results may be difficult to interpret. Some trials of antiarrhythmic drugs and management strategies have had design faults that have complicated the interpretation of the trial data. Clinical trial results are only one component of the body of knowledge that clinicians must use when they plan patient management and prescribe therapies. Data from the basic sciences, other branches of medicine, personal experience, and clinical trials must all be available in order to reach the best decision. It is inappropriate to rely exclusively on the results of clinical trials because individual patients and their problems rarely, if ever, fully match the characteristics of patients enrolled into clinical trials. However, data from good RCTs should form an important base for clinical decision making.