The causes of pain below the chest include heart disease and lung disease, as follows:1. Heart disease: angina pectoris and myocardial infarction are common, patients mostly have paroxysmal or persistent pain on the left side of the chest after strenuous exercise, overexertion, or emotional stimulation, and electrocardiograms and myocardial necrosis markers can be used to make a clear diagnosis.2. Lung disease: pneumothorax, pleurisy, and pneumonia are common, and the chest pain is mostly related to respiration and movement, aggravated by deep inhalation and alleviated or relieved by breath holding, and CT of the lung can make a clear diagnosis.3. Chest pain is mostly related to respiration, aggravated by deep inhalation and alleviated or relieved by breath-holding, and can be diagnosed by CT of lungs.3. Phytoneurological dysfunction: it is related to mental tension and stress, and there is no abnormality in objective examination.