Under what circumstances is cardiac angiography required. First, unexplained chest pain, which cannot be diagnosed by non-invasive tests, and clinical suspicion of coronary artery disease. Second, unexplained arrhythmias, such as intractable ventricular arrhythmias or new-onset conduction block, sometimes require coronary angiography to exclude coronary artery disease. Third, unexplained left heart insufficiency is mainly seen in dilated cardiomyopathy or ischemic cardiomyopathy, and coronary angiography is needed to differentiate between the two. Fourth, percutaneous coronary intervention, or coronary artery bypass grafting, postoperative recurrence of angina pectoris. Fifth, congenital heart disease and valve disease before major surgery, age 50 or about 50-70 years old, patients prone to combined hypertension and hyperlipidemia have coronary artery malformation or atherosclerosis, can be intervened at the same time of surgery.