The CABG Patch Trial is a multicenter, randomized controlled clinical trial to test the hypothesis that implantable cardioverter defibrillator (ICD) therapy will improve survival in coronary heart disease patients at high risk of death, especially arrhythmic death, i.e., patients with severe left ventricular dysfunction who also have a marker of arrhythmic risk (positive signal averaged ECG). To address this question, patients with coronary heart disease will be enrolled if they are having coronary artery bypass graft surgery, are less than 80 years of age, have left ventricular ejection fraction less than 0.36, and have a positive signal averaged ECG. This group is similar to the patients who already have had a sustained ventricular arrhythmia and therefore have an indication for ICD treatment under current guidelines. Also, the group has a high probability of experiencing death during followup. The treatment and control groups are well matched for another important aspect of chronic coronary heart disease - risk for ischemic events. Having both groups revascularized at the beginning of the trial has the potential advantage of sharpening the endpoint, i.e., a smaller proportion of all deaths are expected to be ischemic, and a larger proportion are expected to be arrhythmic, a pathophysiology that is addressed superbly by the treatment under study. Enrolled patients will be randomized during surgery to receive an ICD or not. We plan to randomize 800 patients, half to the control group and half to the ICD group. Patients will be followed for an average of three years after randomization. The CABG Patch Trial has 80%-85% power to detect a hypothesized 40% reduction in the 40-month hazard rate for all-cause mortality in the ICD treated group. In addition, The CABG Patch Trial will: document any morbidity of ICD treatment; evaluate the effects of ICD therapy on quality of life; and compare the health care costs of ICD treatment with those in the control group. In the narrowest interpretation, the results will apply to high risk coronary heart disease patients undergoing CABG surgery. Also, the results should apply substantially to patients who satisfy the current indications for ICD treatment and to some other high risk coronary heart disease patients who have not yet had an arrhythmic event.