The coefficient of microcirculatory resistance (IMR) is a quantitative measure of coronary microcirculatory resistance. The coefficient of microcirculatory resistance is the inverse of the distal coronary pressure at maximal congestion divided by the mean conduction time. In the presence of meaningful epicardial coronary lesions and collateral circulation, myocardial blood flow is the sum of coronary and collateral blood flow, and the measured IMR value may be higher than the true IMR value. There is no standardized IMR value in the world, but an IMR of less than 25 is usually considered normal, and an IMR of more than 40 is associated with a higher incidence of clinical events. IMR has the advantages of being unaffected by changes in hemodynamic parameters such as heart rate and blood pressure, being reproducible, and being unaffected by the degree of epicardial coronary stenosis. If there is any abnormality in the test, it is necessary to consult a doctor for a clear diagnosis and standardized treatment.