Electrophysiologically guided operations for ventricular tachycardia (VT) have been directed exclusively by activation time maps. Even with computer-assisted mapping, extensive editing is required, which prolongs the duration of the operation and which may introduce significant error. In contrast, potential distribution maps can be constructed in less than 3 minutes and can be viewed as a movie of developing and receding potentials. In 4 patients undergoing operation for VT, endocardial mapping was performed using form-fitting electrodes containing 160 points. A computerized mapping system, capable of simultaneously recording 256 channels of data, was used to analyze data and to display potential distribution maps sequentially at 1-millisecond intervals as a color movie. A total of eight morphologies of sustained VT were mapped. The mean VT cycle length was 340 ± 40 milliseconds (range, 274 to 394 milliseconds). In 3 patients with ischemic heart disease, four VT morphologies originated from the subendocardium. All were successfully ablated with cryoablation alone or in conjunction with aneurysmectomy and endocardial resection. A fourth patient with VT secondary to cardiomyopathy had multiple morphologies and received an implantable cardioverter defibrillator. Potential distribution maps correlated well with the concomitant activation time maps. Thus, potential distribution mapping provides a rapid and accurate means of identifying the site of origin of VT facilitating intraoperative mapping in patients undergoing surgical ablation.