Inclusion Criteria:

• 1. Women and men with signs and symptoms of myocardial ischemia and angina or angina equivalent (chest pain, abnormal stress testing, abnormal noninvasive testing) or microvascular angina (MVA) which is defined as angina and ischemic ECG changes without organic obstructive stenosis or epicardial spasm of the coronary arteries
• 2. No obstructive coronary artery disease performed within the previous 24 months (\<50% luminal obstruction in one or more coronary arteries on angiography).
• 3. Age \> 18 years old
• 4. Competent to give informed consent

Exclusion Criteria:

• 1. Obstructive CAD ≥ 50% luminal diameter stenosis in ≥ 1 epicardial coronary artery,
• 2. Acute coronary syndrome (defined by the ACC/AHA criteria, Braunwald 2000),
• 3. Primary valvular heart disease clearly indicating the need for valve repair or replacement;
• 4. Patients with concurrent cardiogenic shock or requiring inotropic or intra-aortic balloon support;
• 5. Prior or planned percutaneous coronary intervention or CABG or prior acute MI in prior 30 days;
• 6. Prior non-cardiac illness with an estimated life expectancy \<4 years;
• 7. Unable to give informed consent;
• 8. Chest pain with a non-ischemic etiology (e.g.,pericarditis, pneumonia, esophageal spasm);
• 9. Contraindications to adenosine or Regadenoson (Lexiscan)
• 10. Women and men with intermediate coronary stenoses (\>20% but \<50% luminal diameter stenosis assessed visually at the time of angiography) will undergo clinically indicated IVUS testing based on the judgment of the operator; those determined to have flow FFR or obstructing stenosis will be excluded from the overall study.
• 11. Heart failure (NYHA Class III or IV on treatment)
• 12. LV dysfunction (ejection fraction \<40%)
• 13. Documented obstructive myocardiopathy