Ribs under the left armpit are painful when breathing. Rib fracture, intercostal neuralgia, pleurisy, cardiogenic diseases and so on are most often considered. 1. Rib fracture: trauma and other causes lead to rib fracture, manifested by local tissue swelling, pain, deep breathing or change position when the pain can be aggravated. 2. Intercostal neuralgia: Infection, trauma and other causes of intercostal nerve damage, manifested as one or more intercostal nerve innervated area of the pain, mostly along the intercostal nerve in a band-like distribution, pinprick or burning pain, coughing, deep breathing, sneezing pain can be aggravated. 3. Pleurisy: if pleurisy occurs in the rib area under the left armpit, under the stimulation of inflammatory factors, chest pain and chest tightness can occur, and the pain can be aggravated by deep breathing or coughing. 4. Cardiogenic diseases: such as angina pectoris, caused by imbalance of blood supply and demand in the heart, manifested as chest pain, chest tightness, chest tightness, etc., which can spread to the whole precordial area, and is easily triggered by emotional excitement or after exertion. The left side of the armpit under the rib cage gasping for breath are also seen in other diseases, it is recommended that patients timely to the regular hospital, so as not to delay the condition.