In clinical work, we often see reports with a diagnosis of differential cyanosis. Differential cyanosis, also known as differential cyanosis, is usually due to congenital heart disease, right-to-left shunt due to congenital heart disease, or ductus arteriosus, producing a milder upper body cyanosis and a more severe lower body cyanosis. In addition, it may be accompanied by dissection of the aortic arch or persistent pulmonary hypertension. Because the blood saturated with oxygen due to the pulmonary artery does not pass through the unclosed ductus arteriosus into the descending aorta, and the blood from the upper extremity comes from the hyperoxic left heart. That is, there is a heavier bruising in the upper body and a lighter bruising in the lower body. Once this happens, you should go to the hospital for consultation as well as treatment in a timely manner.