Possible causes of left-sided stomach pain include functional dyspepsia, gastric ulcer, chronic gastritis, gastric cancer, coronary heart disease and so on. 1. Functional dyspepsia: functional dyspepsia is a kind of functional gastrointestinal disease, there is no obvious organic change in all kinds of examination and laboratory tests, and the patients mainly manifested as fullness after meals, distension and bloating of the upper abdomen, hidden pain, burning sensation, loss of appetite and so on. 2. Gastric ulcer: it is the result of the imbalance between gastric acid, pepsin and gastric mucosal barrier, and most patients have Helicobacter pylori infection. The main manifestation of epigastric pain, the nature of hidden pain, dull pain, distension, burning pain, etc., with a certain rhythm, often in the postprandial episodes. 3. Chronic gastritis: chronic gastritis is a chronic inflammation of the gastric mucosa caused by a variety of reasons, and Helicobacter pylori infection, long-term use of some drugs, autoimmune and other factors related to the patient’s main manifestations of non-specific gastrointestinal symptoms, such as vague pain in the epigastric region, discomfort, abdominal distension, nausea. Vomiting, etc. 4. Gastric cancer: The majority of gastric cancer patients have no obvious specific symptoms in the early stage, which can be manifested as non-specific digestive symptoms such as abdominal pain, bloating, dyspepsia, loss of appetite, etc. In the late stage, it can be manifested as emaciation and anemia. 5. Coronary heart disease: acute myocardial infarction and other patients with coronary heart disease will sometimes be atypical symptoms for the first manifestation, such as epigastric pain, shoulder pain, toothache, etc., so epigastric pain should be excluded from coronary heart disease. It is recommended to go to the hospital as soon as possible to get a clear cause of the disease and then treat it accordingly.