There are five main possibilities for vague pain in the left side of the chest: First, cardiac system diseases, such as coronary heart disease or myocardial infarction, manifested as pain in the left anterior chest area, accompanied by posterior back radiating pain, which can be relieved by sublingual nitroglycerin. Secondly, costochondritis, which occurs in the 2nd-4th rib cartilage on the left side, the pain is mostly stabbing and distributed along the rib edge, and often increases after cold or exertion. Third, cystic hyperplasia of the breast, common in 30-50 women, manifested as breast swelling and pain and nodule-like changes in breast enlargement, and the degree of pain is mostly related to the menstrual cycle. Fourth, acute mastitis, mostly in lactating women, is characterized by red, swollen, hot and painful breasts, and may have fluctuating lump formation. Fifth, breast cancer, manifested as breast paroxysm pain, may appear breast skin folds or orange peel signs. After the appearance of a burst of pain in the left breast, you should seek medical attention promptly, do not believe in the prescriptions to avoid the progress of the disease and cause serious clinical complications.