The pain in the left side of the middle of the sternum, i.e. the precordial area, may be caused by aortic coarctation, myocarditis, acute myocardial infarction and other diseases, but also can be seen in trauma, pleurisy, costal chondromalacia and so on. 1. Aortic coarctation: caused by the presence of entrapment hematoma in the aorta of the heart, due to the different sections of the aorta where the entrapment hematoma is located, there can be different clinical symptoms, such as precordial pain, left arm pain, abdominal pain and so on. 2. Myocarditis: myocardial inflammation caused by viral infection or immune factors, etc., which may be manifested as chest pain, fever, limb weakness and other symptoms. 3. Acute myocardial infarction: myocardial ischemia and necrosis caused by obstruction of coronary blood flow, often sudden onset, the most typical symptom is the squeezing pain in the precordial region, accompanied by dyspnea, panic and other symptoms. 4. Trauma: trauma leads to local soft tissue injury or rib fracture, manifested as chest pain, chest tightness, etc., and localized skin lesions or bruises can be seen. 5. Pleurisy: such as tuberculous pleurisy, the inflammation invades the left pleura, chest pain, chest tightness, mostly accompanied by low-grade fever, cough, fatigue and other symptoms. 6. Costal chondritis: there is no clear cause, can be secondary to trauma, infection, etc., manifested as swelling and pain in the front chest wall. Sternal middle left pain can also be seen in other causes, it is recommended that patients seek timely medical treatment, so as not to delay the condition.