The goal of this observational study is to explore the incidence and effect on prognosis of coronary microvascular dysfunction in patients present of stable anginal symptoms, a clinical indication for invasive coronary angiography, and no hemodynamically significant epicardial coronary artery disease, defined as fractional flow reserve (FFR) >0.80.

Inclusion Criteria:

• presence of stable anginal symptoms, a clinical indication for invasive coronary angiography, and no hemodynamically significant epicardial coronary artery disease, defined as fractional flow reserve (FFR) >0.80

Exclusion Criteria:

1. acute myocardial infarction
2. significant valvular heart disease
3. advanced chronic kidney disease
4. patients with significant epicardial coronary artery stenosis (>70% in major vessels by diagnostic coronary angiography) needing percutaneous coronary intervention
5. patients unable to provide written informed consent

Patients present of stable anginal symptoms, a clinical indication for invasive coronary angiography, and no hemodynamically significant epicardial coronary artery disease, defined as fractional flow reserve (FFR) >0.80