 The primary objective of this study is to test the hypothesis that therapy directed primarily by a T wave alternans TWA test, measured non-invasively during exercise, is equivalent to therapy directed by an electrophysiological study EPS in predicting spontaneous ventricular tachyarrhythmic events VTEs in patients with ischemic heart disease, left ventricular dysfunction, and asymptomatic non-sustained ventricular tachycardia NSVT. In the absence of any previous life-threatening ventricular arrhythmia i.e., for primary prevention, ICD implantation is currently indicated in patients with ischemic heart disease, left ventricular dysfunction, asymptomatic non-sustained ventricular tachycardia, and a positive EPS. The objective of this study is to demonstrate that a TWA test directed therapy is equivalent to EPS directed therapy in guiding ICD implantation for the purpose of primary prevention of sudden cardiac death SCD in patients with ischemic heart disease, left ventricular dysfunction, and asymptomatic non-sustained ventricular tachycardia. 