Atrioventricular nodal reentry tachycardia (AVNRT) is one of the most frequent mechanisms of paroxysmal supraventricular tachycardia. In these patients tachycardia is maintained due to anterograde conduction through a slow pathway and retrograde conduction to the atrium via a fast pathway. We present herein our experience in ablation of the slow pathway. Since January 1993, 30 consecutive patients with AVNRT underwent attempted catheter ablation of the slow pathway. Mean age was 35 +/- 3.7 years. All patients had symptomatic tachycardia and six had history of syncope. Electrophysiologic studies revealed AVNRT in all patients, in addition, two patients had a left accessory pathway. Slow pathway ablation was performed with a Mansfield 7 F catheter, guided by both fluoroscopic positioning and endocardial signals. A mean of 13 bursts were applied. In the 30 patients conduction through the slow pathway was interrupted, and thus tachycardia was no longer inducible. Retrograde conduction post ablation was evaluated in 17 of the 30 patients, significant changes were observed in three of them. One patient developed second degree AV block and a permanent pacemaker was implanted. Another patient had recurrence of tachycardia three months post ablation. After a second attempt she is arrhythmia free. Patients have been followed for a mean of 15.7 +/- 2.5 months and are asymptomatic in the absence of antiarrhythmic therapy.