Pain under the left chest may be lung, heart and stomach, these three organs appear disease can be manifested as pain under the left chest. First, pneumonia: when the left lower pneumonia, the patient may appear fever, cough, cough sputum, left chest pain and dyspnea and other symptoms, it is recommended to do chest radiographs or lung CT to make a clear diagnosis. Second, coronary heart disease: coronary heart disease, including angina pectoris and acute myocardial infarction, patients with coronary heart disease will appear below the left chest pain, usually paroxysmal. Angina pectoris pain is shorter, usually lasts a few minutes, the degree of pain is mild, usually after rest or containing nitroglycerin can be relieved. Acute myocardial infarction pain lasts longer, usually more than 15 minutes, or even up to several hours, severe pain, accompanied by sweating, shortness of breath and other symptoms, it is recommended to do an electrocardiogram and myocardial enzyme profile. Third, gastric diseases: gastritis, gastric ulcer, gastric cancer, patients may have pain under the left chest, accompanied by nausea, vomiting, acid reflux, belching and other symptoms, it is recommended to do gastroscopy for a clear diagnosis.