Tetralogy of Fallot is the most common cyanotic congenital heart defect in newborns, affecting 3 to 6 babies in every 10,000 births in Canada. It involves four structural heart problems present at birth that reduce the amount of oxygen in the blood. Babies with this condition often have a bluish tint to their skin, lips, and fingernails — a sign doctors look for right away in the delivery room. The good news is that with early diagnosis and surgical treatment, most children go on to live healthy, active lives.
What Is Tetralogy of Fallot?
Tetralogy of Fallot is a combination of four heart abnormalities that develop before birth. These four problems work together to reduce the flow of oxygen-rich blood throughout the body. The word “tetralogy” simply means a group of four — and in this case, all four defects are connected and affect how the heart pumps blood.
The four abnormalities are:
Pulmonary stenosis: A narrowing that blocks blood flow out of the right ventricle toward the lungs.
Ventricular septal defect (VSD): A hole in the wall between the heart’s two lower chambers.
Overriding aorta: The main artery (aorta) sits over the hole in the heart wall instead of its normal position.
Right ventricular hypertrophy: The right side of the heart becomes thickened and enlarged from working too hard.
Sometimes a fifth defect — a hole between the upper chambers — is also present. Doctors call this combination the “Pentalogy of Fallot.” However, the core diagnosis and treatment remain largely the same.
Because oxygen-poor blood mixes with oxygen-rich blood inside the heart, not enough oxygen reaches the rest of the body. This is what causes the bluish skin colour that doctors call cyanosis. According to Mayo Clinic’s overview of tetralogy of Fallot, this condition accounts for about 10% of all congenital heart defects worldwide.
What Causes Tetralogy of Fallot?
In most cases, tetralogy of Fallot appears without a clear cause. Doctors describe this as “sporadic,” meaning it does not typically run in families. However, research suggests that both genetic and environmental factors play a role during early pregnancy.
Genetic Factors
Children with certain chromosomal conditions have a higher risk of developing tetralogy of Fallot. These include Down syndrome and DiGeorge syndrome — a condition involving heart defects, low calcium levels, and immune system problems. Genetic studies suggest the cause is multifactorial, meaning several factors combine rather than one single gene being responsible.
If a parent had tetralogy of Fallot themselves, there is a 1 to 5% chance their child will also have the condition. It also appears slightly more often in boys than in girls.
Prenatal Risk Factors
Several factors during pregnancy may increase the risk of a baby being born with this heart defect. These include:
Rubella (German measles) or other viral infections during pregnancy
Poor nutrition during pregnancy
Drinking alcohol during pregnancy
A mother’s age over 40 at the time of birth
Diabetes in the mother that is not well controlled
In addition, tetralogy of Fallot often appears alongside other heart or non-cardiac birth defects. For example, a persistent ductus arteriosus or abnormal pulmonary veins may also be present. Therefore, a full cardiac evaluation is always recommended when this diagnosis is made.
Recognising the Symptoms of Tetralogy of Fallot
The symptoms of tetralogy of Fallot range from mild to severe depending on how blocked the blood flow to the lungs is. Some babies show obvious signs at birth. Others may appear healthy at first, with symptoms developing over the first weeks or months of life.
Common Symptoms in Newborns and Infants
The most visible sign is a bluish colour of the skin, lips, and fingernails — especially during feeding or crying. This bluish colour, called cyanosis, happens because the blood reaching the body does not carry enough oxygen. Hospital staff in maternity wards across Canada are trained to spot this immediately after birth.
Other common symptoms include:
Difficulty feeding and poor weight gain
Rapid breathing or shortness of breath
Tiring quickly during feeding
Irritability or prolonged crying episodes
Fainting or sudden limpness
Tet Spells — A Key Warning Sign
One of the most important signs of tetralogy of Fallot is something doctors call a “tet spell.” During a tet spell, the baby suddenly becomes very blue and may cry intensely or become unresponsive. These episodes are triggered by a sudden drop in oxygen levels, often caused by crying, feeding, or physical activity.
Older children with unrepaired tetralogy of Fallot may instinctively squat down when they feel unwell. Squatting increases blood pressure in the legs, which pushes more blood toward the lungs and temporarily improves oxygen levels. Doctors actually consider this squatting behaviour a helpful clue during diagnosis.
As noted by Healthline’s guide to tetralogy of Fallot, tet spells are considered a medical emergency and require immediate attention.
How Is Tetralogy of Fallot Diagnosed?
Tetralogy of Fallot is often detected before birth during a routine prenatal ultrasound. In other cases, doctors diagnose it shortly after delivery based on the baby’s appearance and the presence of a heart murmur. The clinical picture is quite distinctive, which allows doctors to make a preliminary diagnosis quickly.
Diagnostic tests used to confirm the condition include:
Echocardiogram: An ultrasound of the heart — this is the main tool used to confirm the diagnosis and see all four defects clearly.
Electrocardiogram (ECG): Measures the heart’s electrical activity and can show if the right ventricle is enlarged.
Chest X-ray: May show a characteristic “boot-shaped” heart, which is a classic sign of this condition.
Blood oxygen testing (pulse oximetry): Measures how much oxygen is in the blood. Many Canadian provinces now include pulse oximetry as part of routine newborn screening.
Cardiac MRI or catheterization: Used in complex cases to map the heart’s structure in detail before surgery.
Furthermore, because tetralogy of Fallot can occur alongside other structural defects, a full assessment by a paediatric cardiologist is essential at the time of diagnosis.
Treatment Options for Tetralogy of Fallot
The only effective long-term treatment for tetralogy of Fallot is surgery. Medical management can stabilise the baby while waiting for the right time to operate, but it does not correct the underlying heart defects. Most Canadian children with this condition are treated at specialised paediatric cardiac centres, such as those found in major cities like Toronto, Montreal, Vancouver, and Edmonton.
Medical Stabilisation Before Surgery
In newborns who are critically ill, doctors may use a medication called a prostaglandin to keep a blood vessel near the heart open. This helps maintain adequate blood flow to the lungs while the surgical team plans next steps. Prostaglandins can also reduce the urgency of immediate surgery in some cases.
Doctors also work to prevent and manage tet spells. During a tet spell, placing the child in a knee-to-chest position can help restore oxygen levels temporarily. Medications such as beta-blockers may be used to reduce the frequency of these episodes.
Surgical Repair
Most specialists now recommend complete surgical repair before a child turns one year old. Early repair leads to better outcomes and reduces the risk of long-term complications. The surgery closes the hole between the ventricles and widens the blocked passage to the lungs, restoring normal blood flow.
Surgical results in Canada are very good. Mortality rates from the procedure itself are low at experienced paediatric cardiac centres. However, some patients may need additional procedures later in life, such as replacing the pulmonary valve.
What Happens Without Treatment?
Without surgery, the outlook for tetralogy of Fallot is serious. Research shows that without treatment, roughly 30% of affected children do not survive past age two, and 50% do not reach age six. Fewer than 5% reach adulthood. Those who do reach adulthood without repair face a high risk of heart failure, stroke, blood clots in the lungs, and serious heart infections. This is why timely diagnosis and access to surgical care are so important.
For more information on congenital heart conditions and children’s health in Canada, visit Health Canada’s official health information portal.
Life After Surgery for Tetralogy of Fallot
Most children who have successful surgery for tetralogy of Fallot grow up to lead active, fulfilling lives. Many attend school, play sports, and have no major day-to-day limitations. However, lifelong follow-up with a cardiologist is important, as some adults may develop complications years after their initial repair.
Common long-term considerations include:
Monitoring for pulmonary valve problems, which may need repair in adulthood
Watching for irregular heart rhythms (arrhythmias)
Managing the risk of heart failure in later life
Regular echocardiograms and cardiology check-ups
Adults who had tetralogy of Fallot repaired in childhood should be followed by a specialist in adult congenital heart disease (ACHD). Most major Canadian hospitals with cardiac programmes offer this type of specialised care. Provincial health plans generally cover these follow-up visits, so speak with your family doctor about getting a referral.
When to See a Doctor
If your newborn shows any bluish colour around the lips, tongue, or fingernails, seek medical help right away. In Canada, you can go directly to the nearest hospital emergency department or call 911. Do not wait for a scheduled appointment if your child appears to be having a tet spell or is not breathing normally.
For parents who have a family history of congenital heart disease, speak with your family doctor or obstetrician early in pregnancy. Ask about a fetal echocardiogram, which can sometimes detect heart defects before birth. Most provincial health plans cover prenatal ultrasounds, and your doctor can arrange additional testing if there is a concern.
If your child has already been diagnosed and you are waiting for surgery or a specialist appointment, watch closely for changes in skin colour, unusual tiredness, or difficulty breathing. Your local walk-in clinic can help assess a non-emergency concern, but any sudden worsening should be treated as urgent.
Always speak with a qualified healthcare provider before making any decisions about your child’s health. This article is for informational purposes only and does not replace professional medical advice.
Frequently Asked Questions About Tetralogy of Fallot
What is tetralogy of Fallot in simple terms?
Tetralogy of Fallot is a heart condition present at birth that involves four structural problems with the heart. These defects reduce the amount of oxygen in the blood, causing a bluish skin colour in newborns. It is the most common cyanotic congenital heart defect and is treatable with surgery.
Can tetralogy of Fallot be detected before birth?
Yes, tetralogy of Fallot can sometimes be detected during a routine prenatal ultrasound, typically around 18 to 22 weeks of pregnancy. If a concern is found, your doctor may order a fetal echocardiogram for a more detailed look at the baby’s heart. Early detection allows the medical team to plan care before the baby arrives.
Is tetralogy of Fallot curable?
Tetralogy of Fallot is not “cured” in the traditional sense, but surgical repair dramatically improves the heart’s function and most children go on to live normal lives. The surgery corrects the four defects and restores proper blood flow. Lifelong follow-up with a cardiologist is still recommended after repair.
What are tet spells and are they dangerous?
Tet spells are sudden episodes where a baby with tetralogy of Fallot becomes very blue and may cry intensely or lose consciousness. They happen when oxygen levels in the blood drop sharply, often triggered by crying, feeding, or exertion. Tet spells are a medical emergency — call 911 or go to the nearest emergency department immediately.
How common is tetralogy of Fallot in Canada?
Tetralogy of Fallot affects approximately 3 to 6 babies per 10,000 live births, making it the most common cyanotic congenital heart defect in Canada and worldwide. It appears slightly more often in boys than in girls. In most cases, it occurs without a family history of the condition.
Can adults have tetralogy of Fallot that was never repaired?
Adults with unrepaired tetralogy of Fallot are at serious risk of heart failure, stroke, and dangerous heart rhythm problems. Without surgical correction, fewer than 5% of patients historically reached adulthood. Adults in this situation should seek assessment at a centre specialising in adult congenital heart disease (ACHD) as soon as possible.
Key Takeaways
Tetralogy of Fallot
