Lying down after the appearance of the left side of the chest pain is mainly seen in coronary heart disease, lung disease, chest wall disease, digestive system diseases. 1. Coronary heart disease: mainly seen in middle-aged and elderly patients, may have hypertension, diabetes, hyperlipidemia and other risk factors, resulting in coronary artery vascular stenosis, affecting the blood supply to the heart can appear chest pain and discomfort, can be manifested as lying down on the left side of the chest uncomfortable. 2. Lung diseases: most common in pneumonia, pneumothorax, pulmonary embolism, pleurisy, etc., often accompanied by cough, sputum, fever, dyspnea and other symptoms, the patient lying down because of pleural friction or inflammation stimulation and other reasons, the left chest tightness, pain and other discomfort. 3. Chest wall diseases: such as rib fracture caused by trauma, soft tissue injury, costochondritis, intercostal neuralgia, chest wall tuberculosis, chest wall abscess, etc., resulting in damage to muscles, nerves, bones, etc., leading to discomfort in the left chest after lying down. 4. Digestive system diseases: such as esophagitis, gastroesophageal reflux disease, gastritis, gastric ulcer, pancreatitis and other diseases, after lying down, due to gastric acid reflux stimulation of the esophagus, involving pain, and other reasons can appear left chest tightness, pain and other discomfort. It is recommended that the patient should consult the doctor in time to clarify the cause of the disease, and treat the symptoms and causes of the disease.