Sex difference of coronary microvascular dysfunction evaluated by coronary flow reserve will be assessed in patients with non-obstructive coronary artery disease

The investigators will select consecutive patients who experienced chest pain but had no significant coronary artery stenosis (<50% stenosis). Coronary microvascular function will be evaluated by adenosine stress echocardiography. Coronary blood flow velocities will be measured at 1, 2, and 3 min after adenosine infusion.

Sex difference of coronary microvascular dysfunction evaluated by coronary flow reserve will be assessed.

Inclusion Criteria:

• Typical/atypical chest pain or ischemic symptoms including dyspnea
• No significant coronary artery stenosis (<50% stenosis) in coronary angiography or computed tomography

Exclusion Criteria:

• ≥ Moderate valvular heart disease
• Congenital heart disease
• Chronic renal failure (estimated glomerular filtration rate <30 ml/min/1.73m2) or end-stage renal failure undergoing hemodialysis or peritoneal dialysis
• Asthma, chronic obstructive pulmonary disease and primary pulmonary hypertension
• Receiving anticancer drugs
• Vasculitis associated with autoimmune diseases
• Atrioventricular block with more than second degrees, symptomatic bradycardia, cryo-node failure syndrome, Wolff-Parkinson-White (WPW) patients

Consecutive patients who experienced chest pain but with no obstructed coronary arteries (<50% stenosis)