Horseshoe lung (HL) is an infrequent congenital lung anomaly. Its main feature is that the lower lungs on both sides extend behind the pericardium and fuse across the midline, usually accompanied by pulmonary dysplasia. It is reported that 80% of HL is relevant to the abnormal return of some pulmonary veins from the right lung to the inferior vena cava or right atrium (scimitar syndrome). Most patients are within 5 years old, most commonly within 1 year old, but HL may also have no apparent clinical symptoms or mild symptoms. This case is a 36-years-old adult female who developed left chest pain more than a month ago and continued to worsen for 10 days. The patient also had repeated pulmonary infection with cough and expectoration.