The vague pain under the left sternum can be seen in the following cases: first of all, we should consider coronary heart disease, which includes angina pectoris or myocardial infarction, angina pectoris pain lasts for a short time, usually lasts for 15 minutes, and the pain is mild and can be relieved after taking nitroglycerin. Acute myocardial infarction pain lasts longer, often more than 15 minutes, or even up to several hours, and the pain is severe and cannot be relieved by nitroglycerin, it is recommended to do electrocardiogram and myocardial enzyme spectrum examination to clarify the diagnosis; secondly, it can be seen in stomach disease, the patient is accompanied by nausea, vomiting, abdominal distension, acid reflux, belching and other symptoms, it is recommended to do gastroscopy; again, it should be considered lung disease, it can be seen in pneumonia and pleurisy, the patient is accompanied by cough, cough and sputum. Patients with cough, sputum, fever, dyspnea and other symptoms at the same time, it is recommended to do chest X-ray or lung CT for clear diagnosis.