The Blalock–Thomas–Taussig shunt (BTT shunt), previously known as the Blalock–Taussig Shunt (BT shunt), is a surgical procedure used to increase blood flow to the lungs in some forms of congenital heart disease such as pulmonary atresia and tetralogy of Fallot, which are common causes of blue baby syndrome. In the modified Blalock–Thomas–Taussig shunt, a length of artificial tubing typically made from PTFE (Teflon) is sewn between either the subclavian or the carotid artery and the corresponding side branch of the pulmonary artery.