Tetralogy of Fallot (ToF) is made up of a combination of four defects that commonly occur together.
ToF is made up of the following four defects of the heart and its blood vessels:
- Ventricular septal defect. A hole in the wall between the two lower chambers (ventricles) of the heart.
- Pulmonary stenosis. A narrowing of the pulmonary valve and main pulmonary artery.
- Ventricular hypertrophy. The muscular wall of the lower right chamber of the heart (right ventricle) is thicker than normal.
- Overriding aorta. Occurs when the aortic valve, which opens to the aorta, is enlarged and seems to open from both ventricles, rather than from the left ventricle only, as in a normal heart. In this defect, the aortic valve sits directly on top of the ventricular septal defect.
The abnormal flow of blood from the heart into the lungs leads to blood being diverted through the ventricular septal defect (VSD) to the aorta. Blood flow and lung circulation is reduced causing the child to appear blue.
Because a baby with ToF may need surgery or other procedures soon after birth, this birth defect is considered a critical congenital heart defect.