Occasional occult pain on the left side of the chest can occur in normal people and is associated with various insignificant stimulation of sensory nerve fibers. In the pathological state, the causes of vague pain on the left side of the chest include: chest wall tuberculosis, intercostal nerve inflammation, rib injury, soft tissue injury, pancreatitis, pneumothorax, heart disease, etc. In normal people, shortness of breath and muscle fatigue may cause vague pain on the left side of the chest when running and exercising, which can be relieved after resting, so there is no need to worry. If the middle-aged and elderly people have vague pain on the left side of the chest, especially after exertion, they need to exclude the possibility of coronary heart disease and angina pectoris. If a person with a relatively long and lean body has sudden onset of vague pain or stabbing pain on the left side, followed by difficulty in breathing, he should be alert to the occurrence of pneumothorax. In patients with previous tuberculosis, chest wall tuberculosis may occur and invade the nerves causing vague pain. A fan blowing against a position can lead to inflammation of the intercostal nerves. When damaged by external forces, rib fractures and damage to the soft tissues of the chest wall may occur and also cause occult pain. Lesions of the pancreas, duodenum, and common bile duct sometimes also cause hidden pain on the left side of the chest. In conclusion, hidden pain on the left side of the chest may occur occasionally in normal people, but most of the time, one needs to be alert to other diseases such as coronary heart disease, angina pectoris, pneumothorax, intercostal neuritis, etc.