Inclusion Criteria:  Age ≥ 18 years old. Known cardiac ischemia, who are non revascularizable, or have not and will not be undergo coronary intervention for the duration of their participation in the study. Evidence of ischemia from previous clinical tests (echo, nuclear, standard ECG from past 6 months). Left Ventricular Ejection fraction > 40% by echo (evaluated last 3 months). Able to complete a cardiopulmonary exercise test without significant non cardiac limitations, primarily orthopedic. On guideline directed optimal therapy for stable ischemia.  Exclusion Criteria:  Anemia (< 7 mg/dl). Low potassium (< 3 mmol/L). Creatinine (> 5.0 mg/dl or < 0.6 mg/dl). Unable to exercise due primarily to orthopedic limitation. Severe lung disease. Morbid obesity (BMI > 42). Pregnant. Breast feeding. Significant arrhythmia (ventricular tachycardia, ventricular fibrillation, frequent premature ventricular contractions (PVCs), persistent atrial fibrillation, or 2nd or 3rd degree atrioventricular (AV) block). Seizures. Unstable angina. Coronary spasm. Recent myocardial infarction (< 90 days). Recent percutaneous coronary intervention (<90 days).