Whether left coronary atherosclerosis is serious depends on the degree of coronary stenosis caused by atherosclerosis and whether it has caused angina pectoris, myocardial infarction and other serious complications. 1. Degree of stenosis: stenosis of less than 50% is mild stenosis, which can be asymptomatic or mild; stenosis of 50-75% is moderate stenosis, which can be characterized by chest tightness, shortness of breath, dyspnea and even fainting; stenosis of more than 75% is severe stenosis, which is prone to cause myocardial infarction. 2. Complications: atherosclerosis of coronary arteries, if left unchecked, may cause myocardial ischemia, leading to coronary atherosclerotic heart disease, the common types of which are stable angina pectoris, unstable angina pectoris, non-ST-segment elevation myocardial infarction and ST-segment elevation myocardial infarction. Therefore, when coronary atherosclerosis is detected, it is important to go to the hospital in time to clarify the risk factors leading to atherosclerosis, such as hyperlipidemia, hypertension, diabetes mellitus, etc., and to carry out active treatment to avoid progression to coronary heart disease.