Background: In RF ablation of idiopathic left ventricular tachycardia (ILVT), termination of tachycardia was taken as a hallmark of successful RF energy delivery. However, sometimes it is hard to deliver RF energy during on-going VT, especially in patients(pts) with non-inducible ILVT attributable to catheter manipulation. Besides, in those pts, the evaluation of procedural success and ILVT recurrences could be problematic. Furthermore, evaluation of procedural success and VT recurrences could be problematic in those patients. Methods & Results: We tried RFCA in 10 ILVT pts (9 M : 1 F, Age 33.5 짹 7.5) during sinus rhythm because of repeated mechanical trauma of the tachycardia while manipulating the mapping catheter or difficulty of tachycardia induction. We focused on the rhythm changes, especially on repetitive ventricular responses (> 5 consecutive QRS beats) during RF application. The incidence and clinical implications of the repetitive ventricular responses were examined through the results of RF ablation. RF ablation–attempted site was selected in an area where the tachycardia was presumed to be mechanically terminated during catheter manipulation and also showed P-potential. The mean number of RF application was 9.5(짹4.2)/pt. Even though the frequency and QRS morphology of ventricular responses during ablation was variable as the ablation site moved, The repetitive ventricular responses, especially showing very similar QRS morphology to that of clinical VT was noted at least more than once in all patients. There was one pt who received repeated procedure due to recurrence of IILVT 3 days after first procedure. During his first procedure, no repetitive ventricular response was noted but it had been regarded successful because of no re-induction of tachycardia. The mean follow-up period of 10 pts was 15.0 짹 10.3 months. The clinical course of pts having the repetitive ventricular response was favorable to show no recurrence in 9 out of 10 pts. Conclusion: In addition to non-inducibility, the occurrence of repetitive ventricular responses with similar morphology to clinical VT and its disappearance during RF application could be a marker of an appropriate ablation site.