Empagliflozin Versus Sitagliptin Therapy for Improvement of Myocardial Perfusion Reserve in Diabetic Patients With Coronary Artery Disease

Inclusion Criteria: * Men or women at least 19 years of age * Type 2 diabetes mellitus * Stable coronary artery disease * Global myocardial perfusion reserve (MPR) index \< 2.5 * The patient or guardian agrees to the study protocol and the schedule of clinical and dynamic SPECT follow-up, and provides informed, written consent, as approved by the appropriate Institutional Review Board/Ethical Committee of the respective clinical site. Exclusion Criteria: * Contraindications to empagliflozin, Sitagliptin * DPP4 inhibitors or Sodium-glucose cotransporter-2(SGLT2) inhibitors within the previous 4 weeks * Insulin requiring diabetes * Poor glucose control (HbA1C\>10 %) * Acute coronary syndrome * Stent placement within the previous 6 months * Previous coronary artery bypass graft surgery within the previous 6 months * Planned revascularization within 6 months * Heart failure requiring loop diuretics * Severe left ventricular hypertrophy (left ventricular septal wall thickness \> 13mm) * Significant renal disease manifested by creatinine clearance of \< 30 ml/min) * Hepatic disease or biliary tract obstruction, or significant hepatic enzyme elevation (alanine transaminase or Aspartate Aminotransferase \> 3 times upper limit of normal) * Radiopaque material implanted in the chest wall (metal, silicone, etc.) * Contraindication to adenosine stress test * Any clinically significant abnormality identified at the screening visit, physical examination, laboratory tests, or electrocardiogram which, in the judgment of the Investigator, would preclude safe completion of the study. * Patient's pregnant or breast-feeding or child-bearing potential * Expected life expectancy \< 1 year * Unwillingness or inability to comply with the procedures described in this protocol