Coronary angiography (CAG): (1) Coronary angiography is the “gold standard” for the diagnosis of coronary artery disease and can accurately determine the location and degree of coronary artery stenosis and the characteristics of coronary artery lesions. (2) To determine the mode of formation and grading of coronary collateral circulation. (3) To determine the presence or absence of coronary artery spasm. (4) To make a diagnosis of myocardial muscle bridges. (5) To make a definite diagnosis of coronary artery aneurysm and coronary artery malformation.