Two prior studies had compared, in a non-randomized fashion, the predictive accuracy of EPS and HM in treating patients with ventricular tachycardia/ ventricular fibrillation. A retrospective analysis of 44 patients with ventricular tachycardia/ventricular fibrillation who underwent both HM and EPS was performed in which the elimination of ventricular tachycardia on the HM and the suppression of ventricular tachycardia induced during programmed stimulation was the therapeutic goal. The positive and negative predictive value of EPS was found to be 88 percent and 94 percent, respectively. The corresponding values for ECG monitoring were found to be 70 percent and 50 percent, respectively. It was concluded that EPS provided a higher degree of accuracy than HM in predicting the long-term clinical response to drug therapy, over a mean follow-up of 18 months. However, in this study the criterion for judging efficacy by HM was a liberal one and involved only the elimination of ventricular tachycardia.