Inclusion Criteria:  Clinical presentation of chronic ischemic heart disease (IHD), requiring coronary angiography for the diagnosis Absence of obstructive CAD at coronary angiography Age > 18 years Ability to provide a valid informed consent to the study procedure at the time of baseline evaluation  Exclusion Criteria:  Clinical presentation of acute coronary syndrome (ACS) or cardiogenic shock Presence of obstructive CAD with at least 1 significant coronary artery stenosis, defined as diameter stenosis >50% and FFR ≤0.80 (or iFR/RFR ≤0.89) Previous coronary artery bypass grafting (CABG) Left ventricular systolic dysfunction, defined as ejection fraction (EF) <40% Severe valvular heart disease Pregnant or breastfeeding women Known hypersensitivity or contraindication to any of the drugs used for coronary physiology testing (adenosine, nitrates, acetylcholine) Inability or unwillingness to provide a valid informed consent to the study procedure at the time of baseline evaluation