---
title: Tetralogy of Fallot
description: What tetralogy of Fallot is, which four changes in the heart make it up, how it is found, how it is treated in children, how adults are followed up after surgery and when urgent help is needed.
type: disease
aliases:
  - TOF
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Тетрада Фалло
    year: 2024
    url: https://cr.minzdrav.gov.ru/view-cr/39_3
  - tier: guideline
    org: esc
    title: 2020 ESC Guidelines for the management of adult congenital heart disease
    year: 2020
    doi: 10.1093/eurheartj/ehaa554
    url: https://doi.org/10.1093/eurheartj/ehaa554
  - tier: reference
    org: msd-manuals
    title: Tetralogy of Fallot
    year: 2023
    url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/tetralogy-of-fallot
sources_checked: 2026-10-12
review: null
---

Tetralogy of Fallot is a congenital heart defect made up of four features.<Cite n={[1, 2, 3]} />

1. Ventricular septal defect: a large hole in the wall between the right and left ventricles, lying just below the aorta.<Cite n={[1, 3]} />
2. Right ventricular outflow tract obstruction and pulmonary valve stenosis: the path for blood from the right ventricle to the lungs is narrowed.<Cite n={[1, 3]} />
3. Overriding aorta: the aorta is shifted towards the right ventricle and sits astride the defect; less than half of its opening lies over the right ventricle.<Cite n={[1, 2]} />
4. Right ventricular hypertrophy: the muscular wall of the right ventricle is thickened.<Cite n={[1, 2, 3]} />

It is a "blue" (cyanotic) defect: usually the child's lips and skin turn blue, because the blood going to the body does not carry enough oxygen.<Cite n={1} /> When the narrowing is mild, there may be no blueness at rest.<Cite n={[1, 3]} />

<Diagram name="tetralogy-of-fallot">
  <p slot="normal">
    In a normal heart none of the four features is present: the wall between the ventricles is
    intact, the outflow from the right ventricle into the pulmonary artery is wide, the aorta
    arises from the left ventricle and the wall of the right ventricle is not thickened. So blood
    from the right ventricle goes into the pulmonary artery, and blood from the left ventricle goes
    into the aorta.<Cite n={[1, 3]} />
  </p>
  <p slot="disease">
    In tetralogy of Fallot there is a large defect in the wall between the ventricles, the outflow
    from the right ventricle into the pulmonary artery is narrowed, the aorta sits astride the
    defect and the wall of the right ventricle is thickened.<Cite n={[1, 3]} /> The main pulmonary
    artery is often narrower than normal too.<Cite n={[1, 3]} /> Less blood reaches the lungs, and
    some oxygen-poor blood from the right ventricle passes through the defect into the
    aorta.<Cite n={3} />
  </p>
  <p slot="treated">
    After complete repair, the hole in the wall between the ventricles is closed with a patch and
    the path for blood from the right ventricle to the pulmonary artery is widened.<Cite n={[1, 3]} />
    Doctors choose the type of operation according to where exactly the right ventricular outflow
    is narrowed.<Cite n={1} /> After repair the pulmonary valve may leak (pulmonary regurgitation):
    some blood flows back from the pulmonary artery into the right ventricle.<Cite n={[1, 2]} /> Significant leakage
    is almost always seen when the patch crosses the valve ring.<Cite n={2} />
  </p>
</Diagram>

## Why it happens

<Patient>

The defect forms while the heart is developing: one of the partitions inside the heart is displaced, so the outflow from the right ventricle becomes narrowed and a hole is left in the wall between the ventricles.<Cite n={[1, 3]} />

Because of the narrowing, less blood reaches the lungs, and some oxygen-poor blood passes through the hole into the aorta and on to the body, so the blood lacks oxygen.<Cite n={[1, 3]} /> How severe the defect is depends mainly on how narrow the outflow is.<Cite n={[1, 3]} /> About 20% of cases are linked to genetic changes, for example a missing piece of chromosome 22.<Cite n={[1, 2]} />

</Patient>

<Student>

Tetralogy of Fallot is a cyanotic congenital heart defect and a conotruncal anomaly; it is diagnosed in 8–13% of all patients with congenital heart disease (CHD).<Cite n={1} /> Anterior and leftward displacement of the conal (outlet) septum causes infundibular stenosis, and abnormal rotation of the conus arteriosus leads to dextroposition of the aorta, which overrides the ventricular septal defect (VSD).<Cite n={1} /> Right ventricular outflow tract obstruction (RVOTO) may be infundibular, valvular, supravalvular and/or branch pulmonary artery (PA) stenosis, with consequent right ventricular (RV) hypertrophy.<Cite n={2} />

Both ventricles and the aorta form a single haemodynamic system with equal systolic pressures; the right-to-left (venoarterial) shunt, together with the overriding aorta and pulmonary stenosis, causes arterial hypoxaemia.<Cite n={1} /> According to the ESC, about 20% of patients have a genetic syndrome (22q11 microdeletion, trisomy 21, Alagille syndrome and others).<Cite n={2} />

</Student>

## Symptoms

<Patient>

The first signs are blueness (cyanosis) of the lips and fingertips and breathlessness that gets worse during feeding and crying; the child may lag behind in physical development.<Cite n={1} /> In about 20–30% of children with severe narrowing this is seen from the first days of life, and they need emergency surgery; in 70–80%, cyanosis appears towards the end of the first or the start of the second year.<Cite n={1} /> A typical sign is that some children squat during play: in this position the blood carries more oxygen.<Cite n={[1, 3]} />

A dangerous feature is hypercyanotic ("tet") spells. The child suddenly starts breathing fast and deeply, becomes irritable and cries for a long time, and turns more and more blue; a severe spell can lead to limpness, seizures and occasionally death.<Cite n={3} /> A spell can be set off by crying, a bowel movement, play, or the child kicking their legs on waking.<Cite n={3} />

Adults who have had surgery may develop heart rhythm problems, and heart failure becomes much more common with age.<Cite n={[1, 2]} />

</Patient>

<Student>

A hypercyanotic spell consists of paroxysmal hyperpnoea, irritability and prolonged crying, increasing cyanosis, and a softer or absent murmur; peak incidence is at 2–4 months of age.<Cite n={3} /> The mechanism is uncertain: right-to-left shunting probably increases because of greater RVOTO, higher pulmonary vascular resistance and lower systemic vascular resistance.<Cite n={3} />

A harsh systolic murmur is heard at the left sternal border, caused by flow across the pulmonary stenosis; the VSD is usually silent because it is large and has no pressure gradient.<Cite n={[1, 3]} />

</Student>

## How it is diagnosed

<Patient>

A doctor may suspect the defect from blueness, breathlessness and a heart murmur.<Cite n={[1, 3]} /> The main test is an ultrasound scan of the heart (echocardiography) with Doppler: it shows the hole in the wall, the position of the aorta, the thickness of the right ventricular wall and how narrow the outflow is.<Cite n={[1, 3]} /> An ECG and a chest X-ray are also done, and the oxygen level in the blood is measured (pulse oximetry).<Cite n={1} />

</Patient>

<Student>

Transthoracic echocardiography with colour Doppler is recommended for everyone with suspected tetralogy of Fallot and during follow-up; it assesses the size and position of the VSD, the degree of aortic override, the severity of RV hypertrophy, and the length and degree of RV outflow tract narrowing.<Cite n={1} /> Typical ECG findings are right axis deviation, RV hypertrophy and right atrial enlargement.<Cite n={[1, 3]} /> The chest X-ray shows reduced pulmonary vascular markings and a boot-shaped heart.<Cite n={[1, 3]} /> Contrast-enhanced cardiac CT is done when echocardiography is inconclusive; in newborns and infants in the first year of life CT is the method of choice. Cardiac catheterisation is done before surgery when echocardiography findings are ambiguous, and to assess the pulmonary artery branches and collaterals.<Cite n={1} />

After repair, the ECG often shows complete right bundle branch block depending on the surgical approach; cardiac magnetic resonance (CMR) is the method of choice for assessing RV volume and function and pulmonary regurgitation.<Cite n={[1, 2]} />

</Student>

## How it is treated

<Patient>

The main treatment is an operation called complete (corrective) repair: the surgeon closes the hole with a patch and widens the path for blood from the right ventricle to the pulmonary artery.<Cite n={[1, 3]} /> It is usually done in the first year of life; doctors decide when and how to operate based on the child's condition and the structure of the heart and blood vessels.<Cite n={1} /> After timely repair the outlook is good.<Cite n={1} />

Sometimes, for example in newborns with a low birth weight or complex anatomy of the vessels, a palliative (relieving) operation is done first: an extra route for blood to the lungs (a shunt) is created or a stent is placed.<Cite n={[1, 3]} /> Newborns with critical narrowing are given a medicine into a vein before surgery that keeps the arterial duct open; this is a vessel through which blood can reach the lungs.<Cite n={[1, 3]} /> Hypercyanotic spells are treated by doctors; most experts think that even one significant spell means the operation should be done without delay.<Cite n={3} />

After surgery, lifelong follow-up with a cardiologist is needed: with a paediatric cardiologist until 18, then with an adult cardiologist.<Cite n={1} /> After surgery the pulmonary valve often leaks blood backwards, especially if the valve ring was widened during the operation. This is well tolerated for many years, but severe valve leakage gradually stretches and weakens the right ventricle; the valve may then need to be replaced, in some cases through a catheter.<Cite n={[1, 2]} /> See the article on [pulmonary regurgitation](../pulmonary-regurgitation/) for more. Tell the cardiologist in advance about dental and other procedures: protection against endocarditis may be needed.<Cite n={1} />

</Patient>

<Student>

Complete repair (VSD closure and reconstruction of the RV outflow tract) is done as a primary operation when the pulmonary artery anatomy is favourable, usually in the first year of life, or as a second stage after palliation; in asymptomatic patients it is advisable after 3 months of age.<Cite n={1} /> Perioperative mortality for uncomplicated tetralogy of Fallot is under 5%.<Cite n={3} /> Palliative procedures (systemic-to-pulmonary shunts, stenting of the patent ductus arteriosus or of the RV outflow tract) increase pulmonary blood flow and prepare the patient for complete repair.<Cite n={[1, 3]} /> Spells are managed by medical staff: the infant is placed in the knee-chest position, and oxygen, intravenous fluids, benzodiazepines and beta-blockers are given.<Cite n={[1, 3]} />

Follow-up is lifelong, with an ECG and echocardiography once a year and MRI every 2–5 years; the ESC recommends that all adults with tetralogy of Fallot are followed up in a specialised adult CHD centre, in most cases annually.<Cite n={[1, 2]} /> Late complications include pulmonary regurgitation (almost always after a transannular patch repair), residual RVOTO or VSD, aortic dilation, ventricular dysfunction, arrhythmias and sudden cardiac death.<Cite n={2} /> A QRS duration of 180 ms or more is a risk factor for sudden death.<Cite n={[1, 2]} /> Pulmonary regurgitation is the most frequent reason for considering reoperation; a biological pulmonary valve lasts on average 10–20 years, and transcatheter pulmonary valve implantation has become an alternative to open surgery, mainly in patients with a conduit.<Cite n={2} /> For some adults with multiple risk factors for sudden death, an implantable cardioverter-defibrillator should be considered.<Cite n={1} />

</Student>

## When to call an ambulance

A hypercyanotic spell can be life-threatening and needs immediate help.<Cite n={3} /> If a child with tetralogy of Fallot suddenly starts breathing faster and more deeply, is irritable and cries for a long time, turns more and more blue, becomes limp or has a seizure, call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK). Do not wait to see whether the spell happens again.<Cite n={3} />

The Russian Ministry of Health guideline also lists as reasons for emergency hospital admission a sharp increase in blueness and breathlessness, episodes of heart rhythm disturbance and worsening heart failure.<Cite n={1} />

Adults who have had surgery should see a cardiologist as soon as possible if breathlessness, blueness, swelling or an irregular heartbeat appear or suddenly get worse, or if they have lost consciousness.<Cite n={1} />

<Quiz />