The causes of left chest pain are very many, but the more important cases are mainly the following four: First, coronary heart disease, angina pectoris, usually with hypertension, coronary heart disease, diabetes and other underlying diseases, often when the onset of activity, eating too much or emotional excitement, check the electrocardiogram can help clarify the diagnosis. Second, aortic coarctation, often accompanied by hypertension, is manifested by tearing pain in the chest, sometimes the performance of the ECG is normal, the aortic CTA can help to make a clear diagnosis. Third, pulmonary embolism, often with a history of lower extremity fracture or trauma surgery, examination of the veins of both lower extremities, sometimes can find deep vein thrombosis, examination of the pulmonary artery CTA can help clarify the diagnosis. Fourth, pneumothorax, which often occurs suddenly during strenuous activity or exertion, or with a history of chronic lung disease, examination of chest X-ray or chest CT can help to make a clear diagnosis.