The main reasons for the left subcostal pain are: first, the rib cage is considered to be traumatized, resulting in rib fractures, causing pain or pain caused by intercostal neuralgia. Second, the left side of the rib cage belongs to the lungs, may be due to lung diseases, such as pneumonia, pneumothorax, pleurisy, lung tumors caused by the pain. Third, the left side of the rib cage under the heart, there may be an acute myocardial infarction, resulting in pain under the left rib cage. Therefore, in order to know the cause of pain, it is necessary to carry out physical examination and auxiliary examination to understand the condition.