The aim of this study is to investigate the agreement and reproducibility between intravenous and intracoronary adenosine administration during invasive assessment of microvascular function.

Goals of this study are:

1. Agreement and reproducibility between intravenous and intracoronary adenosine administration in the IMR (Index of microvascular resistance) value.
2. Agreement and reproducibility of FFR(fractional flow reserve), CFR (coronary flow reserve), MRR (microvascular resistance reserve), RRR (resistive reserve ratio) and reproducibility of each of these as compared with CFRabs (absolute coronary flow).
3. Time required for IMR measurements

The study is a single-center randomized, cross-over controlled, open label trial to investigate the reproducibility and agreement between intravenous and intracoronary adenosine administration during invasive assessment of microvascular function.

The primary analysis will be on the per-protocol population (i.e. including all patients who are not protocol violators).

Primary endpoint:

1. Agreement and reproducibility between intravenous and intracoronary adenosine administration in the IMR value.

Secondary endpoints:

1. Agreement and reproducibility of FFR, CFR, MRR, RRR and reproducibility of each of these as compared with CFRabs.
2. Time required for IMR measurements
3. Presence and severity of angina, assessed by SAQ(Seattle Angina Questionnaire)-7
4. Assessment of safety: Presence and severity of AV( atrioventricular) block, dyspnea, flush

Inclusion Criteria:

• Chronic coronary syndrome (including patients with anginal equivalents).
• 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)
• Willingness to participate and ability to understand, read and sign the informed consent
• Age>18 years

Exclusion Criteria:

• Age <18 years
• Bronchial asthma, COPD (chronic obstructive pulmonary disease)
• Secondary or tertiary atrioventricular block without prior pacemaker implantation
• Previous CABG (coronary artery bypass graft) 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
• Inability to provide informed consent

Patients and outcome assessors will be blinded to the randomization group.