Objectives: To compare the features of the 12 lead ECG of PVC from the distal free wall and septal RVOT to determine the characteristics of ECG for the localization of the original site and the facilitation of mapping and ablation by the RF. Subject and method: A descriptive study was conducted in 31 PVCs from distal sites of RVOT successfully burned by the RF. Radiographing the right ventricle to locate the original site and then studying the 12 lead ECG in these patients. Result: 9 PVCs from distal free wall (28.03 percent) and 22 PVCs from distal septal RVOT. 100 percent of PVCs had inferior axis, left branch bundle block form and there was no difference between the two study groups. PVCs from distal free wall sites had QRS duration, R wave duration on D1 longer, R wave amplitude on aVF greater than PVCs from distal septal sites. These characteristics to locate the original site of PVCs from free wall RVOT: QRS duration on DI 138 msec
R duration in DI 120msec
R wave wide, with notching form on down - slope on inferior leads (sensitivity: 100 percent,55.56 percent,77.78 percent respectively
specificity: 68.18 percent,77.27 percent,86.36 percent respectively). These characteristics to locate the site of origin of PVCs from septal RVOT: QRS duration on DI 138 msec
R duration in DI 120msec
R wave narrow, without notching form on down - slope on inferior leads (sensitivity: 68.18 percent, 77.27 percent,86.36 percent respectively
specificity: 100 percent,55.56 percent,77.78 percent respectively). Conclusion: The analysis of QRS duration and R duration on DI, R - wave amplitude on aVF and shape of R wave on inferior leads on 12 lead ECG can locate original sites of PVCs from distal free wall and septal RVOT.