Cyanosis in congenital heart disease is the purple skin mucosa, the most common two parts: 1, normal people’s lips are pink, once the lips appear black like purple grapes, suspect whether it is cyanosis; 2, some normal people’s lips are usually black, at this time, you can observe the nails, the nail bed is red under normal circumstances, especially at the junction of nails and skin with half-moon circles. If it is a cyanotic patient, it shows as black and purple. Also, some patients have enlarged finger ends due to prolonged cyanosis, which is called pestle finger, like a drum whip. Cyanosis is mostly caused by cyanotic congenital heart disease, because the abnormal shunt of the heart, right-to-left shunt is non-oxygenated blood, and through the abnormal channel to the oxygenated blood causes cyanosis of the skin and mucous membrane.