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." Vetstream.com. 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.
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Thursday, February 19, 2015