The causes of pain in the lower part of the chest are diseases of the thoracic organs such as angina pectoris, pneumothorax and reflux esophagitis. 1. Cardiovascular system diseases: the more common are angina pectoris and acute myocardial infarction. Angina pectoris and acute myocardial infarction are mainly manifested by episodic chest pain, which is often triggered by physical labor or emotional excitement. 2. Respiratory diseases: the more common is pneumothorax. The causes of pneumothorax include chest trauma, lung disease, etc., which manifests as chest pain and dyspnea. Long-term bedridden patients may have pulmonary embolism, which may also manifest as pain in the lower part of the chest. 3. Esophageal diseases: such as reflux esophagitis, there may be chest pain, chest pain caused by refluxed food irritation of the esophagus, occurring behind the sternum. There may be other causes of lower chest pain, such as thymus gland disease, rib fracture, intercostal neuralgia, and so on. When lower chest pain occurs, it is important to go to the hospital at the first time, to clarify the cause of the disease, early diagnosis and early treatment.