Five patients with recurrent bouts of supraventricular tachycardia proved resistant or became intolerant of both conventional and experimental drugs. These patients were subjected to a new procedure involving delivery of DC shocks to an electrode catheter positioned adjacent to the His bundle. Complete atrioventricular (AV) block was produced in all, one patient died suddenly six weeks after shock therapy, and the remainder had complete AV block with follow-up intervals ranging from four to 12 months. Shock therapy was associated with mild elevations of creatine phosphokinase MB (31 +/- 18 units), but there was no hemodynamic evidence of tricuspid insufficiency. If this new technique proves safe and effective, it should supplant the need for open heart surgical procedures for His-bundle ablation.