Randomized clinical trials are the gold standard for the evaluation of new therapies. However, in the early years of pacing, the observational benefits were so great and the lifesaving benefits to patients so readily obvious that randomized trials were not necessary to prove benefit. As the technology has matured, advances have become more evolutionary than revolutionary, and observational analyses are unable to provide convincing evidence of small-to-moderate benefits. Thus, randomized trials of sufficient sample size are necessary to reliably assess the small-to-moderate effects of advances such as dual-chamber pacing, rate modulation, and mode switching. It is only during the last decade, however, that the evidence base for pacing with regard to randomized trials has begun to emerge. It is unclear whether the emerging results of these clinical trials have affected the clinical practice of pacing.