Hidden pain on the left side of the chest can be seen in breast lesions, heart disease, infectious lesions, trauma and so on. 1. Breast lesions: such as breast hyperplasia, mastitis, etc. Some patients with fibroadenoma of the breast will also have paroxysmal pain. 2. Cardiac lesions: such as angina pectoris caused by coronary heart attack, heart attack, etc., which can be manifested as vague pain in the left side of the chest, chest tightness and other symptoms. 3. Infectious lesions: such as inflammation of the left lung, pleurisy, costochondritis, etc., all of which can cause vague pain on the left side of the chest. 4. Trauma: if the left side of the chest has been impacted, resulting in corresponding parts of the soft tissue contusion or rib injuries, may appear in the left side of the chest vague pain feeling. There are many other causes of pain on the left side of the chest, it is recommended to go to the hospital specialist for further examination, in order to clarify the cause of the disease, and take appropriate treatment measures.