1, the etiology of chest pain: the chest wall tissue structure and organs and tissues in the chest cavity, as well as the diaphragm, some organs under the diaphragm in the role of inflammation, ischemia, trauma, tumor, mechanical compression, physical and chemical stimulation and other factors, can cause chest pain this subjective feeling. Therefore, the main etiological factors include intrathoracic structural lesions, chest wall lesions, subphrenic organ lesions and functional diseases. Characteristics of chest pain: The characteristics of chest pain are mainly described by five aspects, i.e. pain site and radiation site, pain nature, pain duration, triggering factors, relieving factors and accompanying symptoms. (1) site and radiological site: chest pain located behind the sternum often suggests angina pectoris, acute myocardial infarction, aortic entrapment, esophageal disease and mediastinal disease; chest pain with the precordial region as the main pain site is seen in angina pectoris, acute pericarditis, left intercostal neuritis, costochondritis, herpes zoster, etc.; pain in the lateral aspect of the chest often occurs in acute pleurisy, acute pulmonary embolism, intercostal myositis. Liver or subdiaphragmatic lesions can also manifest as right-sided chest pain. Chest pain confined to the apical region or below the left nipple is mostly functional chest pain caused by cardiac neurosis, etc. It can also be colonic splenomegaly syndrome, etc. As with the site of chest pain, the site of radiation is also an important clue to the etiology of chest pain. Chest pain radiating to the neck, jaw, and ulnar side of the left arm is often a typical symptom of cardiac ischemic chest pain, in addition to being seen in acute pericarditis. Chest pain radiating to the back can be seen in aortic coarctation and acute myocardial infarction. Right chest pain radiating to the right shoulder often suggests a possible hepatobiliary or subdiaphragmatic lesion. (2) Nature of pain: quite a few diseases cause chest pain with certain characteristics in terms of pain nature, such as cardiac ischemic chest pain. When the patient describes his chest discomfort as pressure, squeezing, stuffy feeling or “heavy pressure” or “tight band feeling”, it strongly supports that it is myocardial ischemic chest pain, most typically the patient describes his discomfort. The sharp, knife-like pain often supports pericarditis, pleurisy, and pulmonary embolism. Aortic coarctation occurs mostly as a sudden, sharp, tear-like pain that is highly characteristic. Momentary pain that manifests as pinprick-like or electric shock-like pain can be seen in functional chest pain, intercostal neuritis, herpes zoster, and esophageal hiatal hernia. The pain in the chest wall is often clearly localized, while the pain caused by intra-thoracic organ lesions is mostly not clearly localized. (3) Pain time frame: the time frame of pain duration has a strong differential diagnostic value for chest pain, especially for the differentiation of myocardial ischemic chest pain and non-myocardial ischemic chest pain. Chest pain that lasts only for a split second or no more than 15 seconds does not support myocardial ischemic chest pain, but is more likely to be musculoskeletal neuropathic pain, esophageal hiatal hernia pain or functional pain. Chest pain lasting 2 to 10 minutes is more likely to be stable chest pain, while those lasting 10 to 30 minutes are more likely to be unstable angina pectoris. Chest pain lasting more than 30 minutes or even several hours can be acute myocardial infarction, pericarditis, aortic entrapment, herpes zoster, and skeletal pain, which are long-lasting and not easily relieved in a short period of time. (4) Triggering and relieving factors: myocardial ischemic chest pain, especially exertional angina, is mostly triggered by exertion or emotional excitement, and the chest pain can be relieved after resting or taking nitroglycerin due to the reduction of oxygen consumption demand of the heart. Most of the angina pectoris can be relieved within 3 to 5 minutes after taking nitroglycerin, while those not relieved for more than 15 minutes may be myocardial infarction or non-myocardial ischemic chest pain. Chest pain due to esophageal spasm is usually triggered by eating cold liquids, and sometimes it can also come on its own. With the exception of chest pain caused by esophageal spasm, all other non-cardiac ischemic chest pain cannot be relieved by nitroglycerin. Chest pain due to acute pleurisy is often associated with breathing and chest movements, and can be induced to worsen by deep breathing and can be relieved by breath holding. Musculoskeletal and neuropathic chest pains tend to worsen with touch or chest movement. While functional chest pain is mostly associated with depression, hyperventilation chest pain is induced by hyperventilation, and Mallory-Weiss syndrome tends to occur after violent vomiting. It can be seen that understanding the triggering and relieving factors of chest pain can help analyze the possible etiology. (5) Concomitant symptoms: Chest pain caused by different etiologies has different concomitant symptoms. Chest pain with pale skin, profuse sweating, decreased blood pressure or shock can be seen in acute myocardial infarction, aortic coarctation, aortic sinus aneurysm rupture or acute pulmonary embolism. Chest pain with hemoptysis suggests possible pulmonary embolism, bronchopulmonary cancer and other respiratory diseases. Chest pain accompanied by fever can be seen in acute infectious diseases such as lobar pneumonia, acute pleurisy and acute pericarditis. When chest pain is accompanied by obvious dyspnea, it often indicates serious involvement of cardiopulmonary function, such as acute myocardial infarction, pulmonary embolism, lobar pneumonia, spontaneous pneumothorax, mediastinal emphysema and other conditions. Chest pain with dysphagia suggests the presence of esophageal disease. And when the patient with chest pain has obvious symptoms of anxiety, depression and sighing should think of the possibility of functional chest pain such as cardiac neurosis.