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# Tetralogy of Fallot

Tetralogy of Fallot is a congenital heart defect with four features, including a hole between the ventricles, that makes a child's [skin](https://durgical.com/en/anatomy/skin/) bluish.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Interventricular septum](https://durgical.com/en/anatomy/interventricular-septum/)
- [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/)
- [Pulmonary trunk](https://durgical.com/en/anatomy/pulmonary-trunk/)
- [Ascending aorta](https://durgical.com/en/anatomy/ascending-aorta/)
- [Pulmonary anterior cusp](https://durgical.com/en/anatomy/anterior-semilunar-leaflet-of-pulmonary-valve/)
- [Pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/)
- [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/)
- [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/)
- [Subclavian artery](https://durgical.com/en/anatomy/right-subclavian-artery/)
- [Thymus](https://durgical.com/en/anatomy/thymus/)

## In embryology

- [Neural crest cells and their derivatives](https://durgical.com/en/embryology/neural-crest-cells-and-their-derivatives/)
- [22q11.2 deletion (DiGeorge): the third and fourth pouches](https://durgical.com/en/embryology/22q11-2-deletion-the-third-and-fourth-pouches/)
- [Outflow tract: the spiral aorticopulmonary septum and neural crest](https://durgical.com/en/embryology/outflow-tract-the-spiral-aorticopulmonary-septum-and-neural-crest/)
- [Tetralogy of Fallot](https://durgical.com/en/embryology/tetralogy-of-fallot/)
- [Isotretinoin and other retinoids](https://durgical.com/en/embryology/isotretinoin-and-other-retinoids/)

## In the clinical exam

- [Digital clubbing and nail signs](https://durgical.com/en/clinical-exam/digital-clubbing-and-nail-signs/)

## In physiology

- [Physiology of congenital shunts](https://durgical.com/en/physiology/physiology-of-congenital-shunts/)
- [Fetal circulation and the transition at birth](https://durgical.com/en/physiology/fetal-circulation-and-the-transition-at-birth/)

## Why it happens

- [Trisomies 21, 18 and 13, and the 22q11.2 deletion](https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/)

## What it is

A cyanotic congenital heart defect with four features: a ventricular septal defect, right ventricular outflow obstruction, an aorta that overrides the septum and right ventricular hypertrophy. It is the commonest cyanotic heart defect after the newborn period.

## Who gets it

The most frequent cyanotic congenital heart disease. It is associated with 22q11.2 deletion (DiGeorge syndrome) and trisomy 21. Thanks to surgery in infancy, a growing number of adults live with repaired tetralogy.

## Causes

- Anterior and upward deviation of the outlet (infundibular) septum during development, which produces the four features
- 22q11.2 deletion, trisomy 21 and other genetic syndromes
- In most cases no single cause is found

## Risk factors

- Maternal diabetes or uncontrolled phenylketonuria
- Maternal rubella or alcohol use in pregnancy
- Exposure to retinoids in pregnancy
- Family history of congenital heart disease

## Pathophysiology

Outflow obstruction raises right ventricular pressure, so deoxygenated blood crosses the large defect into the overriding aorta (right-to-left shunt) and causes cyanosis in proportion to the obstruction. In a tet spell, the obstruction worsens or systemic resistance falls, the shunt increases and hypoxia deepens. Squatting raises systemic resistance and reduces the shunt.

## Classification

- «Pink» tetralogy: mild obstruction and little cyanosis
- Classic tetralogy with pulmonary stenosis
- Tetralogy with pulmonary atresia: duct-dependent
- Tetralogy with absent pulmonary valve: rare

## Symptoms and signs

- Cyanosis, often increasing over the first months
- Harsh ejection murmur at the upper left sternal border from the outflow obstruction, with a single S2
- Tet spells during crying or feeding: irritability, deep fast breathing and deeper cyanosis
- Squatting after exertion in older children
- Clubbing and polycythaemia if not repaired

## Red flags

- Tet spell: rising cyanosis, fast deep breathing, limpness or loss of consciousness
- Low oxygen saturation on newborn pulse oximetry screening
- Seizures or focal neurological signs in unrepaired disease (brain abscess or stroke)
- Palpitations or syncope in a repaired adult (ventricular arrhythmia)

## Diagnosis

**Clinical**
Cyanosis with an ejection murmur at the upper left sternal border that softens during a spell, and a single S2.

**Tests**
Low pulse oximetry; ECG with right [axis](https://durgical.com/en/anatomy/axis/) deviation and right ventricular hypertrophy; blood count may show polycythaemia; genetic testing for 22q11.2 deletion.

**Imaging**
Echocardiography confirms the diagnosis. [Chest](https://durgical.com/en/anatomy/region/chest/) X-ray shows a boot-shaped heart with reduced lung markings. CT, MRI or catheterisation define the [pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/) and coronaries; MRI follows the [right ventricle](https://durgical.com/en/anatomy/right-ventricle/) after repair.

## Differential diagnosis

- Transposition of the great arteries
- Pulmonary atresia with intact septum
- Tricuspid atresia
- Truncus arteriosus
- Persistent pulmonary hypertension of the newborn
- Eisenmenger syndrome

## Goal of treatment

Relieve cyanosis and spells, perform complete repair in infancy, then follow for life to manage pulmonary regurgitation and arrhythmias.

## Treatment

**Acute**
Tet spell: calm the child, knee-to-chest position and oxygen, then intravenous fluids, opioid sedation, beta-blockers and alpha-agonist vasopressors to raise systemic resistance.

**Acute**
In newborns with severe obstruction or pulmonary atresia, prostaglandin E1 keeps the ductus open.

**Surgical**
Complete repair, usually in the first year: patch closure of the ventricular septal defect and relief of the outflow obstruction.

**Procedure**
When complete repair must wait: a systemic-to-pulmonary shunt (modified Blalock-Taussig) or catheter stenting of the duct or outflow tract.

**Follow-up**
Lifelong specialist follow-up, with pulmonary valve replacement (surgical or transcatheter) for severe regurgitation and rhythm monitoring.

## Complications

- Hypoxic (tet) spells
- Polycythaemia, stroke and brain abscess in unrepaired disease
- Infective endocarditis
- After repair: pulmonary regurgitation and right ventricular dilatation
- Ventricular arrhythmias and sudden death
- Residual defect or obstruction, heart block

## Prognosis

Without treatment, survival into adulthood is uncommon. After repair in infancy most patients reach adulthood with a good quality of life, but many need reinterventions and lifelong follow-up.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the four features of tetralogy of Fallot?

Ventricular septal defect, right ventricular outflow obstruction, overriding aorta and right ventricular hypertrophy.

## What is the classic chest X-ray sign of tetralogy of Fallot?

A boot-shaped heart (coeur en sabot) with reduced lung markings.

## Why does squatting help a child with tetralogy of Fallot?

It raises systemic vascular resistance, which reduces the right-to-left shunt.

## Why does the murmur get softer during a tet spell?

The murmur comes from the outflow obstruction; during a spell less blood crosses it.

## Which genetic deletion is associated with tetralogy of Fallot?

The 22q11.2 deletion (DiGeorge syndrome).

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## Related conditions

- [Ventricular septal defect](https://durgical.com/en/conditions/ventricular-septal-defect/)
- [Patent ductus arteriosus](https://durgical.com/en/conditions/patent-ductus-arteriosus/)
- [Atrial septal defect](https://durgical.com/en/conditions/atrial-septal-defect/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)
- [Infective endocarditis](https://durgical.com/en/conditions/infective-endocarditis/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Tetralogy of Fallot](https://www.ncbi.nlm.nih.gov/books/NBK513288/) (StatPearls (NCBI Bookshelf), 2024).

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Source: https://durgical.com/en/conditions/tetralogy-of-fallot/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/tetralogy-of-fallot/