The pain inside the left rib cage may be related to rib diseases, heart diseases, digestive system diseases, lung diseases and so on. 1. Rib diseases: such as left rib fracture, costochondritis, rib tumor, etc., can cause pain and discomfort at the ribs, which can be clarified by imaging examination. 2. Heart disease: such as angina pectoris, myocardial infarction and other heart diseases may also cause pain in the left side of the rib cage. 3. Digestive system diseases: such as gastritis, gastroduodenal ulcer, etc. can also cause the left side of the rib inside the pain symptoms. 4. Lung diseases: such as pleurisy, pleural effusion, lung tumors, etc. may also show pain inside the ribs. It is recommended to go to the hospital in time to check the symptoms of pain in the left side of the ribs, and to clarify the cause of the pain under the guidance of the doctor’s treatment.