If a patient has distension and pain under the ribs on the left side, the following points should be considered: First, consider that the patient has obvious trauma, such as fracture of the sternum or ribs, contusion, laceration, crush injury and stretch injury of the surrounding soft tissues, which can cause distension and pain on the left side of the ribs, and it will be aggravated with breathing. Secondly, pneumothorax caused by various factors, especially in tension pneumothorax and traffic pneumothorax, the patient will have obvious pain. Third, for cardiogenic diseases, such as unstable angina pectoris in coronary artery disease, severe arrhythmia, or obvious heart failure, there will be ischemia, stenosis, and spasm of coronary artery, in which case there will also be the above symptoms. Fourth, for costochondritis, intercostal neuralgia, or patients with herpes zoster, these conditions will also have symptoms of distension and pain in the above mentioned areas.