In recent years, a catheter technique for closed-chest ablation of the atrioventricular (AV) junction has emerged as a therapeutic alternative for the treatment of supraventricular tachyarrhythmias. The technique involves delivery of one or more direct-current shocks through a cardioverter to a catheter electrode (cathode) that records the His bundle electrogram and a patch electrode (anode) that is placed adjacent to the left scapula. The amount of electrical energy used in each shock ranges from 35 to 500 (usually at least 200) J. Successful ablation is judged by the development of complete AV block produced by the thermal injury at the AV junction. This can be accomplished in approximately 60 percent of patients during a first attempt which includes one or more shocks. Implantation of a permanent pacemaker is mandatory following a successful procedure.