The most common cyanotic congenital heart defect is what?

Tetralogy of Fallot: Tof- ventricular septal defect, (vsd, hole between the right and left ventricles), narrowing of the pulmonary outflow tract (the valve and artery that connect the heart with the lungs), overriding aorta (the artery that carries oxygen-rich blood to the body) shifted over the right ventricle and vsd instead of coming out only from the left ventricle, and thickened right ventricle.

ToF/TGA: As other's mentioned, Tetralogy of Fallot is the most common form of cyanotic congenital heart disease in the US overall/after infancy. In some regions, transposition of the great arteries is the most common in the newborn period.