A patient with a drug-refractory sustained ventricular tachycardia (VT) of nonischemic cause was mapped for the site of VT origin. The intraoperative mapping showed the earliest site of activation of VT on the epicardial surface at which the initial deflection of the local electrogram preceded the onset of the QRS complex of VT by 45 msec. The endocardial mapping could not indicate the site at which the electrogram was found prior to the onset of the QRS complex of VT. However, at the earliest site of the endocardial mapping, VT was entrained without change in the configuration of the QRS complex. After cessation of the rapid pacing, VT resumed at the intrinsic rate and the first post-paced return cycle was identical to each paced cycle length. The interval from the stimulus to the orthodromically captured local electrogram at the pacing site was identical to the cycle length of VT. Catheter ablation from the endocardial side and a cryoablative procedure from the epicardial side failed to eradicate the VT. These findings suggest an intramural site of VT origin and reentrant circuit of which the exit and the entrance face the epicardial and the endocardial surfaces, respectively.