Inclusion Criteria:  Chronic coronary syndrome (including patients with anginal equivalents). Reversible ischemia on non-invasive testing, indication to cardiac catheterization; Indication to the assessment of microvascular function (note: patients will be asked for participation and consented prior to the first measurement of microvascular function, which will be conducted as per clinical indication; only those with evidence of pure or mixed microvascular disease (index of microvascular resistances (IMR)>25 will proceed into the study); Willingness to participate and ability to understand, read and sign the informed consent; Age>18 years  Exclusion Criteria:  Previous CABG with patent grafts to the left anterior descending coronary Epicardial coronary disease (FFR <0.80 with evidence of a focal stenosis) in the left anterior descending territory Severe valvular heart disease Any cardiomyopathy; pulmonary or renal disease Inability to provide informed consent Any disease reducing life expectancy