Tetralogy of Fallot (TOF) factsheet


Tetralogy of Fallot (TOF) is a rare condition where a baby has four different congenital heart defects. 

Congenital heart defects are differences in how the heart grows during pregnancy. There can be differences in different parts of the heart, like the:

  • aorta – the largest blood vessel, responsible for carrying oxygen-rich blood away from the heart to the rest of the body
  • atria – the two top chambers of the heart that receive the blood flowing in 
  • pulmonary arteries – blood vessels that carry oxygen-poor blood from the right side of the heart into the lungs
  • ventricles – the two bottom chambers of the heart that pump the blood back through the body.

Heart defects can change how blood and oxygen flow through the lungs, heart, and body. 

Children with TOF usually do not have enough blood flowing to their lungs. This means the blood pumped from the heart to the rest of the body does not have enough oxygen to keep them healthy.

The four congenital heart defects that cause TOF are:

Ventricular septal defect (VSD)

VSD is when there is a hole between the two bottom chambers of the heart, called ventricles. 

This hole lets oxygen-poor and oxygen-rich blood mix, reducing blood flow to the lungs. 

Pulmonary stenosis

Pulmonary stenosis is when the valve or flap that connects the right ventricle to the pulmonary artery is thicker than usual.

A thicker valve makes the pathways smaller, forcing the heart to work harder than usual to pump blood to the lungs.

Right ventricular hypertrophy

Right ventricular hypertrophy is when the muscle in the wall of the right ventricle is thicker than usual.

Thicker muscle makes the pathways smaller and forces the heart to work harder than usual to pump blood to the lungs.

The heart is a muscle, so the harder it works, the thicker it becomes.

Overriding aorta

Overriding aorta is when the aorta is larger than usual and sits in a slightly different position.

A normal aorta starts at the left ventricle, while an overriding aorta starts at the left and part of the right ventricle. 

This means oxygen-poor blood gets pumped back through the body.

 Signs and symptoms

Signs and symptoms of TOF will look different depending on how severe the defects in your child’s heart are.

Signs and symptoms can include:

  • cyanosis – when there is a bluish colour in the skin, lips, tongue, and nails 
  • shortness of breath and rapid breathing, especially during feeding or exercise
  • poor weight gain
  • getting very tired, very easily  
  • irritability
  • crying for longer than expected
  • heart murmur – when there is a whooshing sound in the heart caused by the force of the blood flowing
  • fainting
  • clubbing of the finger and toenails – an abnormal, rounded nail bed shape.


TOF is diagnosed:

  • during pregnancy with results from ultrasound scans of your baby’s heart
  • at birth, if your baby is showing the blue colour of cyanosis
  • in the first few weeks after your baby is born, when any other signs or symptoms are noticed.

Your baby will see a child specialist doctor called a paediatrician in the hospital after birth. If the paediatrician thinks they may have a heart condition, they will: 

  • check any signs and symptoms
  • do physical examination 
  • order tests and scans to check the heart.

Tests and scans used to get more information about your baby’s heart and blood vessels include:

  • hyperoxia test - where your baby breathes in 100% oxygen for 10 minutes before blood is taken to check the oxygen levels  
  • pulse oximeter – where a small sensor is clipped onto your baby’s fingertip, toe, or ear to measure levels of oxygen in the blood 
  • electrocardiogram (EKG) - an ultrasound that sees how blood moves through the heart
  • chest X-ray – where a type of radiation is used to get an image of the structure of the heart
  • cardiac catheterisation – where a thin, flexible tube is inserted through a vein into the heart to give information about the structure, blood pressure and blood oxygen levels.   

Your child will be referred to a heart specialist or cardiologist to treat and manage TOF.


TOF is treated with surgery to repair the heart defects. 

Surgery is usually done soon after birth. The type of surgery used and the timing can depend on: 

  • how severe the heart defects are
  • your child’s symptoms
  • how healthy your child is
  • how much your child weighs.

Your child’s doctor will talk to you about the most appropriate surgery to use and what age surgery will happen.

Temporary surgery

Temporary surgery is usually done in babies who are too small to have full surgery. The aim is to do small repairs that will improve blood flow to the lungs until your baby can have a complete repair.

In temporary surgery, the doctor will insert a:

  • stent - a tiny wire mesh tube that props open the part of the heart that carries blood out of the right ventricle to the lungs
  • shunt – a small tube between the aorta and the pulmonary artery that lets more blood travel to the lungs for oxygen. 

The stent and shunt usually stay inside the heart until the complete repair surgery.

Temporary surgery for TOF is a closed heart procedure. This means the surgeon does the procedure without opening your child’s chest.

Complete repair

Complete repair of TOF is usually done around 4 - 6 months of age or whenever your baby is strong enough for surgery.

A complete repair involves:

  • closing any holes or gaps with a patch
  • making the narrowed areas of the ventricles and arteries wider
  • removing the stent or shunt from the previous surgery.

Complete repair of TOF is an open-heart surgery. This means the surgeon will need to open your child’s chest to access and repair their heart.


Hypercyanotic spells

Hypercyanotic or Tet spells happen when the oxygen levels in your child’s blood drop quickly. 

In hypercyanotic spells, your baby will: 

  • have a sudden deep blue or grey colour in their skin, nails and lips that lasts for several minutes
  • seem floppy or unwell
  • cry for longer periods
  • increase how deep and fast they are breathing.

A child with TOF might have a hypercyanotic spell when they are:

  • crying
  • feeding
  • upset or agitated
  • waking up early in the morning.

Spells are rarely life-threatening and commonly happen in babies aged 2-6 months before they have had surgery.

Generally, it is normal for a baby to have a slight blue tinge when they are crying or cold. 

It is usually not a hypercyanotic spell if:

  • their skin colour only changes while crying, feeding, or upset
  • their skin goes back to normal after they stop crying
  • they otherwise seem well.

See your local doctor as soon as possible if you are worried or unsure about hypercyanotic spells.

Supporting your child through a hypercyanotic spell

Hypercyanotic spells can be distressing, but they will generally get better when your child feels comforted and settled. 

You can help your baby recover from a hypercyanotic spell by:

  1. picking them up and soothing them to lower their heart rate and the amount of oxygen they are taking in
  2. cuddling them with their knees tucked up against their chest to help increase the amount of blood getting to the lungs.

Toddlers and older children sometimes squat automatically during a spell, which can help increase the amount of blood getting to their lungs. 

You should still soothe and comfort your child and support them if they need help raising their knees against their chest.  

Your child’s skin and nail colour should slowly return to normal as they settle. Let your child’s cardiologist know when the spell happened and the trigger.

Call triple zero (000) for an ambulance if your child is having a spell and:

  • not settling
  • not returning to normal
  • still having difficulty breathing.

Long-term complications of TOF

Most babies who have a complete TOF repair will recover well after surgery. 

Your child will need to continue having regular check-ups with their cardiologist throughout their life to make sure they are healthy, growing well and managing any complications from the condition. 

Complications can include:  

  • holes in the wall between the ventricles that can continue to leak after surgery 
  • a larger than normal right or left ventricle that doesn’t work properly
  • arrhythmias - irregular heartbeats 
  • coronary artery disease – where substances in the blood build up inside the artery, making the inside stiff and narrow
  • enlargement of the ascending aorta – where a bulge forms in the aorta, causing it to become weak and at risk of tearing.
Last updated Monday 29th January 2024


This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024