Pain underneath the left chest could be pain in the heart, lungs, intercostal nerves, and skin. It may be coronary heart disease, bronchopneumonia, intercostal neuritis or herpes zoster, respectively. 1. Coronary heart disease: the early manifestation of coronary heart disease is left chest pain in the precordial area, often during labor, can be manifested as dull pain or sharp pain, often accompanied by panic. 2. Bronchopneumonia: when the lung infection is more obvious, it can invade the surrounding pleura, thus triggering chest pain. In particular, pneumonia in the left lower lung can cause pain under the left chest. 3. Intercostal neuritis: Inflammation of the intercostal nerves in the lower part of the left chest can also cause pain under the left chest. 4. Herpes zoster: Herpes zoster is usually distributed along the intercostal nerves, so if herpes zoster occurs on the left side of the lower chest, there may also be pain in the corresponding area. There are other reasons for pain under the left chest, such as aortic aneurysm, esophagitis, etc. can appear in the corresponding area of pain. Chest pain can be triggered by serious illnesses, so once it occurs, please seek medical attention as soon as possible to identify the cause and cooperate with your doctor for aggressive treatment if necessary.