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Tetralogy of Fallot (ToF) is the most common cyanotic congenital heart disease beyond infancy. It consists of four cardinal anatomical abnormalities that lead to right-to-left shunting and systemic desaturation.
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The combination of a VSD with Pulmonary Stenosis, with the Aorta "Overriding" (sitting 'astride') the VSD and with RV Hypertrophy is termed "Tetralogy of Fallot". The obstruction to flow into the lungs leads to blood being diverted through the VSD to the aorta. Flow in the lung circulation is reduced and the child appears 'Blue' (Cyanosed).
Cardiology : Fallots Tetralogy. Rch.org.au. Published 2025. Accessed July 11, 2025. https://www.rch.org.au/cardiology/heart_defects/fallots_tetralogy/
Four key defects:
| Component | Description |
|---|---|
| 1. ‣ | Large, non-restrictive, usually membranous |
| 2. RV outflow tract obstruction (RVOTO) | Subvalvular (infundibular) ± valvular or supravalvular |
| 3. Overriding aorta | Aorta straddles the VSD, receiving blood from both ventricles |
| 4. ‣ | Secondary to outflow tract obstruction |