Left-sided chest pain after lying down is mainly seen in coronary heart disease, lung disease, chest wall itself disease, as follows: 1, coronary heart disease: mainly seen in elderly patients, can appear in the heart blood supply is insufficient. Patients may have high blood pressure, coronary heart disease, high blood fat and other risk factors, resulting in narrowing of the heart blood vessels, affecting the blood supply to the heart can appear chest pain, check the electrocardiogram, cardiac ultrasound can help to clarify the diagnosis; 2, lung disease: the most common in pneumonia, pneumothorax, pulmonary embolism, pleurisy, etc., the patient has the other characteristics of respiratory diseases, such as accompanied by coughing, coughing up phlegm, or pain associated with respiration, check the chest CT, pulmonary artery CT, etc. can help to clarify the chest pain. CT of chest, CT of pulmonary artery, etc. can help to make a clear diagnosis; 3. Diseases of the chest wall itself: for example, inflammation of the chest wall and other factors cause pain in the muscles, nerves and bones, and the patients take pain-relieving medicines to help alleviate the symptoms.