Pain on pressure in the left side of the chest may be caused by a rib fracture, especially after trauma, which may result in a fracture of the left rib. The fracture of the left side may be accompanied by damage to the spleen, which requires prompt CT examination of the abdomen and observation of the patient’s vital signs, and if the heart rate increases and blood pressure decreases, it indicates possible bleeding in the abdominal cavity. If there is a ruptured spleen, emergency splenectomy is required. If there is no fracture and there is pressure pain in the left upper abdomen, it may be caused by a stomach disease, such as gastric ulcer or gastric cancer. Gastric ulcer has relatively severe pain, sometimes accompanied by black stool, and can be clarified by gastroscopy. Gastric cancer is relatively milder in pain and has a longer history, accompanied by symptoms such as weight loss and black stool, so gastroscopy should also be performed to obtain pathology to further clarify the diagnosis. Gastric ulcer can be treated conservatively by internal medicine, but if it is gastric cancer, radical tumor surgery is needed.