Cardiac syndrome X encompasses heterogeneous groups of individuals who present with typical exertional angina pectoris, positive results during exercise and normal coronary arteries on angiography. Nowadays it remains unclear that the mechanisms are responsible for the episodes of angina pectoris in patients with cardiac syndrome X. A large number of clinical research show angina pectoris may be caused by transient myocardial ischemia. Reduced coronary blood flow reserve caused by coronary microvascular dys...