Cyanosis is a condition in which the lips, fingers, and toes appear blue. It happens in some people with congenital heart defects that cause the blood to circulate abnormally.

In people with congenital heart defects, cyanosis can happen if the defect allows oxygen-poor blood from the right side of the heart to enter the left side of the heart directly, instead of traveling to the lungs for more oxygen. In the left side of the heart, the oxygen-poor blood mixes with oxygen-rich blood to be pumped through the body.

Oxygen-poor blood is not as bright red as oxygen-rich blood. The low oxygen level in the blood is what makes the lips, fingers, and toes look blue.

Congenital heart defects that cause cyanosis include

• Tetralogy of Fallot
• Transposition of the great arteries
• Truncus arteriosus
• Tricuspid atresia
• Pulmonary atresia
• Total anomalous pulmonary venous connection
• Hypoplastic left heart syndrome
• Double Outlet Right Ventricle (DORV)