Twelve patients with supraventricular tachycardia refractory to medical management were treated with catheter ablation (fulguration) of the atrioventricular (AV) conduction system followed by pacemaker implantation. All 12 patients had initially 3 degrees AV block. In ten patients it was permanent. One patient had a permanent 1 degree AV block and left bundle branch block. In one patient with initial 3 degrees AV block AV conduction resumed. No major complications were seen. At follow-up, the mean observation period was 15 months (range 3-57 months). All ten patients with permanent 3 degrees AV block were free of arrhythmic symptoms and without any medication. The patient with permanent 1 degree AV block was free of symptoms and arrhythmia, but died 16 months after the ablation. The patient with relapse of the AV conduction continued to have arrhythmic symptoms, but ECG did not confirm arrhythmia. It is concluded that catheter induced 3 degrees AV block is a safe and efficient treatment of patients with supraventricular tachycardia refractory to medical treatment.