Twenty-four patients who underwent transvenous catheter ablation of the atrioventricular (A-V) junction between November 1982 and February 1987 were followed from 18-72 months (mean 47.9) to assess the long term efficacy and safety of the procedure. All had severely symptomatic supraventricular tachyarrhythmias refractory to standard treatment. Atrioventricular conduction was abolished in 23 patients, 22 having permanent pacemakers implanted. Conduction has recovered, though it is modified, in one patient who is asymptomatic on digoxin. Four patients have died; one suddenly 20 months following the procedure, one of progressive heart and liver failure due to hemochromatosis, and two of a stroke. Four patients have had complications related to permanent pacing; one patient has required generator replacement and one patient ventricular lead replacement, one patient had asystole and one patient had a pacemaker-related tachycardia. Two patients remain symptomatic but improved by the procedure. Seventeen patients are free of their original symptoms, 11 having no intervening morbid events. These results demonstrate that patients with severely symptomatic supraventricular tachyarrhythmias may gain long term symptomatic relief from the procedure, but permanent pacing is a cause of significant morbidity and there is a small incidence of late sudden cardiac death.