Background It has been reported that the origin site of idiopathic ventricular arrhythmias from left or right outflow tract can be judged from the transition of R/S on precordial lead of surface ECG.This paper reports 35 patients with idiopathic premature ventricular contractions (PVCs) from left or right outflow tract Methods All the patients had no structural heart diseases.The ECG characteristics in 35 patients who underwent radiofrequency catheter ablation of LVOT or RVOT origin of PVCs were analyzed.