Left breast swelling and pain for 3 years may be caused by breast cystic hyperplasia, breast fibroadenoma, coronary artery disease, etc. Patients should seek medical treatment in time to clarify the cause of the disease. 1. Breast cystic hyperplasia: cysts formed by high expansion of the lobules and ducts of the breast, patients will have breast swelling and pain, which will be aggravated before menstruation and relieved after menstruation, and some of the patients will have nipple overflow, these people should keep their moods happy, and use progesterone, danazol, and other medications for treatment when necessary. 2. Breast fibroadenoma: If the left breast is swollen and painful for 3 years with a localized smooth, painless lump with clear boundary, then it should be considered as breast fibroadenoma, which can be removed through surgery. 3. Coronary heart disease: patients with coronary heart disease will also have chest swelling and pain, which may be mistaken as left breast swelling and pain in female patients, and such people will also be accompanied by chest squeezing sensation, dyspnea and other symptoms, which can be used under the guidance of the doctor, such as nitroglycerin and other drugs. Meanwhile, left breast swelling and pain may also be seen in breast cancer, plasma cell mastitis, granulomatous mastitis and other diseases. There are many causes of breast swelling and pain, for patients who have breast swelling and pain for 3 years, it is recommended to go to the hospital in time, after a clear diagnosis under the guidance of the doctor reasonable treatment.