Left abdominal pain under the ribs may be caused by gastric diseases such as chronic gastritis, gastric ulcer, etc. It may also be caused by heart and lung diseases, costochondritis and other diseases. 1. Gastric diseases: patients with chronic gastritis may have pain in the left upper abdomen, which may be accompanied by nausea, vomiting, acid reflux and other symptoms; patients with gastric ulcer may have pain in the left upper abdomen after eating. 2. Heart disease: patients with stable angina and myocardial infarction may also have atypical left abdominal subcostal pain. 3. Lung disease: patients with left-sided lung infection may have left abdominal subcostal pain, which may be accompanied by cough, fever, sputum and other symptoms. 4. Costal chondritis: patients with costal chondritis may have left abdominal subcostal pain, and pressure on the costal cartilage area may cause tenderness. Patients with left abdominal subcostal pain are advised to go to the hospital and ask the doctor to make a judgment, and should not make a blind judgment on their own.