Background: Paroxysmal supraventricular tachycardia (PSVT) is a common problem and radiofrequency catheter ablation (RFCA) is an effective tool for its treatment, so the present study was designed to determine the efficacy of RFCA in the treatment of PSVT in Shaheed Modarres hospital, 1999-2000. Materials and methods: In a quasiexperimental study, 72 patients were included. Firstly, brief electrophysiologic study was performed to determine the mechanism of arrhythmia, then radiofrequency energy was delivered. Slow pathway ablation was used in all cases with atrioventricular nodal reentrant tachycardia (AVNRT), however, transseptal approach was the primary strategy for ablation of the left sided accessory pathway in atrioventricular reciprocating tachycardia (AVRT). Radiofrequency - related complications were AV node block, CVA, pneumothorax, and deep vein thrombosis. All patients were followed for at least 3 months after ablation for recurrence of arrhythmia. Results: The study population included 42 females and 30 males with the mean age of 42±14.5 years. Diagnosis of arrhythmia was A VNRT in 37(51.4%) and A VRT in 35(48.6%). RFCA was successfully performed in 33(89.2%) and 22(62.9%) cases of A VNRT and A VRT group, respectively (p<0.05). RFCA related complications were noted in 3(8.1 %) patients of the A VNRT and 2 (5.7%) patients of A VRT group, respectively. Recurrence of arrhythmia was reported in 2 (6%) patients of A VNRT group, and 1 patient of A VRT group. Success rate of RFCA in A VNRT and A VRT was progressively increased from 77.8% and 44.4% during the first six-month of the study to 100% and 69% during the last six-month of the study, respectively (p<0.05). Meanwhile, patients with more frequent attacks of arrhythmia had greater chance of successful ablation when compared with patients with less frequent attacks (82.6% vs. 60%, p=NS). Conclusion: RFCA is a safe and a highly successful approach for the treatment of PSVTs especially in A VNRT, which has acceptable recurrence rate and minimal complications. We have concluded that the success rate is affected by site of accessory pathway and frequency of attacks.