The main organ in the left side of the chest is the left lung, and the heart is also on the left side of the chest, and most people have the esophagus on the left side of the chest, and it is connected to the stomach at the bottom of the chest. Therefore, if there is discomfort in the left side of the chest, you should be alert to the symptoms caused by diseases of the left side of the lungs and the heart, as well as the esophagus or the stomach. If chest pain occurs on the left side of the chest, be especially alert to whether it is caused by coronary heart disease or angina pectoris, and gastritis, gastric ulcer, esophagitis and other diseases may also produce symptoms similar to angina pectoris in the left side of the chest and upper middle abdomen.