A symptom limited maximal exercise tolerance with measurement of peak oxygen consumption (VO2) will be performed to assess patient's maximal aerobic capacity. The Naughton protocol will be used. Exercise will continue until limiting symptoms are present, but will be stopped if patient develops sustained arrhythmia, cyanosis, dizziness, decrease in blood pressure or an ataxic gait. Patients who develop angina or claudication limiting exercise capacity will be excluded from further evaluation or participation. Peak oxygen consumption on this test must be < 20 ml/kg/min for a patient to be eligible for this study.