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

An uncommon cardiac defect called “Tetralogy of Fallot” is a devastating birth defect in dogs. It’s estimated by UC Davis that Tetralogy of Fallout affects 1 in 4,000 dogs. However, their website also says, “This is probably an underestimate because some severely affected dogs almost assuredly die at a young age before a veterinarian examines them.” 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.

Symptoms of Tetralogy of Fallot
Most cases are first seen in young dogs between two and eight months of age. Most affected dogs are purebred. While some dogs may have no clinical signs, the puppy may have difficulty breathing, be less active than littermates or have little exercise tolerance. There may be cyanosis (blue or purple color to skin) and a failure to grow and develop normally1.

Diagnosis of Tetralogy of Fallot
The diagnosis involves a number of diagnostic tests including:

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

Prognosis of Tetralogy of Fallot
Without palliative surgical treatment, the prognosis is poor with most dogs dying before a year of age2.

Treatment approaches include:

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

Most surgical approaches are palliative (purely pain reducing) some resulting in better response than others. Successful surgical repair can completely resolve clinical signs associated with the defect2.

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

Questions to ask your veterinarian

  • I have a three-month-old Keeshond puppy that 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 puppy’s gums 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. Orton, EC, K. Mama, P. Hellyer, and TB Hackett. "Open Surgical Repair of Tetralogy of Fallot in Dogs." National Center for Biotechnology Information. U.S. National Library of Medicine. Web.


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Reviewed on: 
Thursday, February 19, 2015