Background: The epicardial side near the cardiac vein is known as the common focus of ventricular tachyarrhythmias (VTs), specifically in patients without structural heart disease. We sought to determine the characteristics and outcome of catheter ablation of VTs which originated from the great cardiac vein (GCV), in comparison with other VTs from LV outflow tract (OT) or aortic cusps (ACs). Methods: Among 157 patients with VTs who underwent catheter ablation, 34 patients with idiopathic VTs which showed the earliest activation from the LVOT were analyzed. 9 patients with VTs in close proximity to GCV were compared with 25 patients who showed the earliest activation at the endocardial LVOT (n=6) and ACs (n=19). Results: In 9 patients (male 3, mean age: 43.2 years) with VTs, of which earliest activation was identified by mapping inside GCV, successful ablation was done at the endocardial anterior mitral annulus in 4 patients, via subxiphoid pericardial puncture in 4 patients, and within the GCV in 1 patient. Ablation within the GCV was difficult due to acute rise of impedance (>400 ohm) during ablation, but it was overcome by rapid ventricular pacing during ablation. Time to maximal depolarization of precordial QRS on ECG was significantly prolonged for the VTs from the epicardium and within the GCV, compared to endocardial origins (108.9ms vs 61.8ms, p<0.05). VTs were recurred in 2/4 patients who have ablated through pericardial puncture, although the frequency of VPC on Holter ECG was markedly reduced (VPC burden 23%���4%, 61%���3%). Other patients showed no recurrence for the mean follow up of 22.6 months. 25 patients (male 15, mean age 44.3 years) showed the earliest activation above the AC (12 left AC, 7 right AC) and below the AC (4 aortomitral continuity, 2 LVOT septum). Successful ablation was done by conventional ablation catheter and 2 (from left AC) VTs were recurred. Conclusions:.Coronary venous or percutaneous epicardial mapping with distinctive precordial ECG assessment facilitated identification of epicardial LVOT VTs. But higher recurrence rate of these VTs after epicardial ablation is challenging, which warrants further technologic advancement.