Tetralogy of Fallot is a heart birth defect that occurs during development of a fetus in the womb.

Tetralogy of Fallot has four key features:

• Ventricular septal defect:
• A hole in the septum that separates the ventricles
• Pulmonary stenosis:
• An obstruction in blood flow from the right ventricle to the lungs
• Overriding aorta:
• The opening to the aorta communicates with the ventricular septal defect. This causes oxygen-poor blood to be pumped to the body.
• Right ventricular hypertrophy:
• A thickened and enlarged right ventricle