Tetralogy of Fallot in Cats: A Rare but Serious Birth Defect

An uncommon cardiac defect called “Tetralogy of Fallot” is a devastating birth defect of cats1. The condition includes a group of four defects. According to the American Heart Association, those are:

  • A hole between the lower chambers of the heart
  • An obstruction from the heart to the lungs
  • The aorta (blood vessel) lies over the hole in the lower chambers
  • The muscle surrounding the lower right chamber becomes overly thickened

The condition results in reverse flow of blood resulting in a lack of oxygenated blood in the circulation1. It's extremely uncommon in cats and no particular cause has been postulated, but since it is congenital there is likely a genetic component involved.

Symptoms of Tetralogy of Fallot
While uncommon in dogs it is even less frequently reported in cats. Most cases are first seen in kittens at around six months of age. There may be cyanosis (blue or purple color to skin) and a failure to grow and develop normally1. Tetralogy of Fallot is the most common of rare diseases that produce cyanosis as a main finding. It is said to make up 6% of feline congenital heart defects2.

Diagnosis of Tetralogy of Fallot
The diagnosis involves a number of diagnostic tests from simple and readily available to very sophisticated and requiring specialist involvement. These include:

  • Radiography
  • Electrocardiography
  • Echocardiography
  • Laboratory blood tests
  • Cardiac catheterization

Several cases of polycythemia (excess red blood cells) have been associated with Tetralogy of Fallot. Polycythemia may result in seizures.

Prognosis of Tetralogy of Fallot
Without surgical treatment for the pain, the prognosis is poor with most cats dying before a year of age1.

Treatment approaches include:

  • Medical management
  • Attempts to dilate valves using balloon catheters and surgical management

Most surgical approaches are done to relieve pain with some resulting in better response than others. Successful surgical repair can completely resolve clinical signs associated with the defect4.

Prevention of Tetralogy of Fallot
Because of the probable congenital basis of this condition, genetic considerations are important. Avoid breeding the parents of affected kittens.

Questions to ask your veterinarian

  • I have a three-month-old kitten who can barely find the energy to walk across the room? My veterinarian told me there could be a heart problem and wants me to see a specialist. What do you think?
  • My kitten’s ears sometimes appear blue. What could it be?

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.


  1. "Case 29: Tetralogy of Fallot Chapter from "Small Animal Cardiovascular Medicine" Online." UC Davis. Web.
  2. Brownlie, Serena, Dr., Phil Fox, Dr., and Penny Watson. "Tetralogy of Fallot." Web.
  3. DJ Brockman, DE Holt, JW Gaynor, and TE Theman. "Long-term Palliation of Tetralogy of Fallot in Dogs by Use of a Modified Blalock-Taussig Shunt." National Center for Biotechnology Information. U.S. National Library of Medicine, 1 Sept. 2007. Web.

Reviewed on:

Thursday, February 19, 2015

10 Rare Genetic Cat Diseases

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Leila Hadziabdic is a Master’s student in Molecular Microbiology, Microbial Ecology and Immunobiology. Always led by her genuine and deep love for all animals, Leila has been surrounded by pets her whole life. She joined the pet genomics company Basepaws in 2017 after earning her Bachelor’s degree in Genetics. Her job is to research and write feline genetic and health-related content, including this Canine Journal exclusive discussion about rare feline genetic disorders and how Cat DNA tests can help us dig into their health history.

Ambulatory electrocardiographic study of the frequency and cause of ventricular arrhythmia after correction of tetralogy of fallot

Ambulatory 24-hour electrocardiographic monitoring with a Holter recording system was performed in 100 patients after repair of tetralogy of Fallot. The incidence and severity of ventricular arrhythmia (VA) were studied relative to operative age, follow-up period after corrective surgery, hemodynamic data, ventricular function and operative method. Significant VA (Lown grade 2 to 4) was detected in 41 patients. Patients with significant VA (group I) were older (11.7 ± 10.0 years old) at operation than those without VA (group II) (5.5 ± 5.8 years, p

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Diagnosing and treating right ventricular hypertrophy

Right ventricular hypertrophy treatment will be decided once a diagnosis and cause is confirmed. The diagnosis usually begins with a physical exam as well as an open discussion with the doctor. Sometimes, just a physical examination can detect if a person has an enlarged heart. If the heart is not functioning properly, it makes sounds that are detectable with the doctor’s stethoscope. Getting a full medical history from the patient can also be very helpful since some heart problems can be inherited. If there is a family history of heart disease, it can put a person at a higher risk of developing RVH.

An x-ray of the chest or an electrocardiogram can show the extent of heart enlargement. Sometimes the ECG is done twice to ensure an accurate reading was taken. Some doctors believe the best way to detect right ventricular hypertrophy is through an echocardiogram. This is a test that uses ultrasound on the heart to take precise measurements of the thickness and size of the heart muscles.

Treatment for right ventricular hypertrophy can include prescription medications such as ACE inhibitors, beta-blockers, and diuretics. These address the symptoms of the condition. For example, beta-blockers are often suggested to help control blood pressure levels, while diuretics are used to remove excess fluid from the body.

There may be other medications that the doctor recommends based on the specific cause of your RVH. There are also implantable devices, including pacemakers and defibrillators, that can be used to help regulate heartbeat.

While it is true that right ventricular hypertrophy can be life threatening, there are literally thousands of people with the condition that are living a relatively normal life. Since pulmonary hypertension is the most common cause of RVH, many cardiac specialists focus on getting the word out about lifestyle and self-management. While medical interventions can’t cure pulmonary hypertension, lifestyle adjustments can help improve the condition.