The Catheter Ablation Registry (CAR) evolved from a pilot study, the Percutaneous Cardiac Mapping and Ablation Registry (PCMAR) formed in 1983. There were scientific limitations in this voluntary registry. Further prospective studies were needed to better define this procedure, and a multicenter international prospective cohort study was designed to allow a rapid assessment of ablation's dangers and potential usefulness. Results from the study were used to guide physicians as to which patients would and would not benefit from these new procedures.