Fascicular tachycardia (FT) arising from the left posterior fascicle, one of the most common forms of idiopathic ventricular tachycardia (VT), is considered benign. Herein is presented our experience of a 25-year-old man presenting with palpitation, dyspnea and dilated cardiomyopathy due to drug-refractory FT who was successfully treated with radiofrequency catheter ablation. Echocardiography showed a dilated left ventricle (LV, 71 mm at end-diastole, 67 mm at end-systole) and decreased ejection fraction (18%). The 12-lead ECG showed a wide-QRS tachycardia (cycle length: 440 msec), with a monophasic R wave in the lead V1, left axis deviation and atrioventricular dissociation. The His-bundle electrogram revealed that the His potential preceded the ventricular activity with an abnormally short HV interval (15 msec) and dissociation of the atrial and ventricular activities. Endocardial mapping during the VT demonstrated that the Purkinje potential preceded the ventricular activity and was earliest at the upper posterior septum of LV, where the tachycardia was ablated with radiofrequency (RF) energy (30 W for 30 sec). The patient remained asymptomatic over a 6 months follow-up and the LV has returned to normal (51 mm at end-diastole, 34 mm at end-systole, ejection fraction: 62%).