Pain under the left side of the chest needs to be looked at: i. Whether it is a man or a woman, and for men it needs to be identified as high risk, intermediate risk or low risk. High-risk pain in the left side of the chest muscle in men can have the following 4 diseases: 1, acute myocardial infarction; 2, acute aortic dissection tearing the left side of the chest muscle; 3, left tension pneumothorax; 4, acute pulmonary embolism. The above four high-risk factors must go to the hospital immediately. Second, chest pain in men at intermediate risk are unstable angina, acute pneumonia, pulmonary infection, pleural effusion, pleurisy and other conditions. Third, low-risk chest pain can be herpes zoster, costochondritis, and osteoarthritis, all of which can cause pain in the left chest and below. Finally, if a woman has pain in the left chest and below, in addition to the factors mentioned above for men, she should also take into account the problem of breast disease, such as lobular hyperplasia of the breast, acute mastitis, and breast tumors, among other factors.