Angina pectoris usually lasts for a few minutes or ten minutes, and those that last for a few seconds are generally not angina pectoris. Those that last for several hours without relief and are accompanied by sweating, weakness and other systemic symptoms may be acute myocardial infarction. What exactly does angina feel like? Usually, it is a feeling of suffocation and constriction, which is often described by patients with typical clinical symptoms as: “tightness in the chest”, “a big stone seems to be pressing on the chest”, “something seems to be blocking the throat “. It is worth emphasizing that angina is often not a pins-and-needles or knife-like pain, nor is it unbearable pain that tosses and turns, and in most cases patients do not describe it as “angina. Acute myocardial infarction symptoms are similar to those described above, but are more severe and may be accompanied by a sense of fear of dying, or by sweating and seated breathing. Many patients have misconceptions about the symptoms of angina pectoris and often ignore some typical symptoms, leading to delayed treatment. Therefore, it is necessary to understand the symptoms of typical angina pectoris. The typical area of angina pain is located in the left anterior thoracic region and is lamellar, not limited to a certain point, but may spread to the jaw, the left upper limb, and sometimes to the back. In atypical patients, especially those with combined diabetes, the location can be variable due to peripheral nerve damage, and discomfort in the area from the jaw to above the umbilicus cannot exclude the possibility of coronary artery disease, and should be taken seriously to avoid missing the diagnosis. Acute heart attack and angina pectoris have the same location. Angina pectoris generally lasts for a few minutes or ten minutes, and those that last for a few seconds are generally not angina pectoris; those that last for several hours without relief and are accompanied by general symptoms such as heavy sweating and weakness may be acute myocardial infarction, while those whose pain lasts for several hours or even days are generally not angina pectoris or heart attack. Predisposing factors for angina include climbing hills, stairs, full meals, emotional excitement, lifting heavy objects, etc. Symptoms appear during physical activity, and patients are often forced to stop their activities. Unstable angina can strike at rest, suggesting severe myocardial ischemia. Acute heart attack is preceded by a course of stable angina or unstable angina, or the first attack is an acute myocardial infarction without any previous symptoms. If the attack of angina pectoris occurs during heavy physical activity, it can be relieved after being forced to stop resting, and it can also be relieved quickly with nitroglycerin. If nitroglycerin is not effective, it is possible that the symptom is not angina pectoris, but also severe myocardial ischemia such as acute infarction. A significant proportion of angina symptoms are not typical, and even experienced cardiologists have difficulty in making accurate judgments based on symptoms alone. ECG is simple and easy to perform and has high diagnostic value for acute heart attack, but limited value for chronic coronary heart disease. The diagnostic significance of ECG for chronic coronary heart disease mainly lies in the detection of changes, that is, the comparison between ECG at the time of chest pain and ECG without chest pain, if there are obvious ischemic changes, it is meaningful to diagnose coronary heart disease and locate the ischemic area, while some “T wave changes” which have not changed for years and years are not necessarily meaningful. It is easy to label a “patient” as having coronary artery disease, leading to misdiagnosis. At present, invasive coronary angiography is still the gold standard for diagnosing coronary artery disease, and together with non-invasive tests such as exercise plate test, stress myocardial nuclear imaging, coronary CT, etc., it is not difficult to diagnose coronary artery disease.