The ability to localize the sites of origin of arrhythmias or those sites critical to their maintenance or their life-threatening consequences has provided the potential for ablating these arrhythmias by delivering shocks through catheters at these critical sites. The capability of treating various arrhythmias by the delivery of shocks through catheters placed at specific intracardiac sites is being studied. These techniques are being evaluated for the creation of atrioventricular blocks to control the ventricular response during supraventricular arrhythmias and for the ablation of bypass tracts and foci of ventricular tachycardia. Complications, including cardiac rupture, and variable success rates make it imperative that such studies only be done by well-trained electrophysiologists. As current techniques evolve, catheter ablation may prove to be a reasonable alternative to pharmacologic or surgical management of patients with disabling arrhythmias.