BACKGROUND: The catheter ablation using radiofrequency(RF) energy in patients with AV nodal reentrant tachycardia(AVNRT) has been proved as a safe and effective nonpharmacologic therapeutic modality. The selective ablation of slow pathway is now becomming a standard treatment in patients with AVNRT because of its high success rate and negligible AV block risk. In our study, we demonstrated the feasibility, success rate and complications of selective radiofrequency catheter ablation of fast pathway or slow pathway for the treatment of AV nodal reentrant tachycardia. METHODS: Among patients diagnosed as AVNRT by electrophysiologic study, total 21 patients (M : F=11 :10, mean age ; 39 years old) were included in this study. Selective RF ablation of fast pathway was performed in 9 patients and selective RF ablation of slow pathway in 12 patients. The RF generator used in this study was Osypka HAT 200 model and catheters were 6F or 7F steerable catheters with 4 mm distal tip. RESULTS: The successful selective abation was achieved in 18 of 21 patient(86%). The success rate of selective ablation of fast pathway was 67%(6/9 patients) and that of slow pathway was 100%(12/12). The complication(complete AV block) was occurred in one patient in slective ablation of fast pathway but there was no AV block in selective ablation of slow pathway. During follow-up, there was one recurrence in patients treated by selective ablation of fast pathway(mean F/U : 17 months) but there has been no recurrence yet in patients treated by selective ablation of slow pathway(mean F/U : 6 months). The procedural feasibility between two ablation methods in terms of total procedure time, fluoroscopic time and number of RF applications was not differrent significantly. CONCLUSION: The RF ablation in patients with AV nodal reentrant tachycardia is a safe and a effective nonpharmacologic therapeutic modality. Especially, the selective RF ablation of slow pathway is a promising therapeutic modality in patients with AV nodal reentrant tachy cardia.