MASTER I - Microvolt T Wave Alternans Testing for Risk Stratification of Post MI Patients

Inclusion Criteria: * Patients indicated for an ICD with a history of heart attacks * LVEF \<= 0.30 as measured by a radionuclide study, angiography or quantitative echocardiography within 3 months prior to enrollment Exclusion Criteria: * Patients with electrocardiographically documented sustained ventricular tachycardia, ventricular fibrillation or prior cardiac arrest (Class I indications) * Patients who have undergone an electrophysiologic study with ventricular stimulation or a MTWA test within 1 year prior to enrollment * Patients with medical conditions that preclude the testing required by the Investigational Plan or limit study participation * Patients unable to complete MTWA testing requirements due to current atrial fibrillation or flutter * Patients unable to exercise and for which alternative modalities (pacing or pharmacological stress) used for MTWA testing are not available * Patients who have experienced an MI within 1 month prior to enrollment * Patients with advanced cerebrovascular disease per physician's assessment * Patients classified as NYHA Class IV at time of enrollment * Patients who have undergone cardiac revascularization within 3 months prior to enrollment or are scheduled for cardiac revascularization at the time of enrollment * Patients with a life expectancy of less than 1 year * Patients with prior ICD * Patients unable to complete follow-up visits at the study center * Patients who are enrolled or intend to participate in another clinical study that would compete with the study objectives (assessment will be the responsibility of the Clinical Trial Leader with guidance from the Executive Committee)