One of the most obvious symptoms of tetralogy of Fallot is a bluish tint to the skin (cyanosis, or blue baby when occurring in infants) of a baby or young person. The skin, lips, fingernails and tongue are often blue or otherwise discolored, especially after exertion (which for babies is most often during feeding time). The condition may also cause periods of profound cyanosis, when the outflow of blood from the right ventricle is nearly blocked. These are called tet spells, and should be treated immediately.

Other symptoms include:

In some cases, infants with tetralogy of Fallot have other defects, such as a patent ductus arteriosus, that may temporarily allow oxygen-rich blood to circulate the body. This may reduce the appearance of symptoms in the early stages of life.