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This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

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Tetralogy of Fallot is a rare congenital defect of the heart with 3 separate developmental abnormalities, and one compensatory change :

    1. Transposition of the aorta from it's normal position entering the left side of the heart, to the right so that it sits over the ventricular septum
    2. Pulmonic stenosis
    3. A subaortic ventricular septal defect - often large
    4. Right ventricular hypertrophy (secondary change)

Tetralogy of Fallot is caused by a genetically inherited defect

Breed Occurrence
Tetralogy of Fallot has been reported in several breeds including English Bulldogs , Fox Terriers, Keeshonds (a polygenic trait in this breed) , Poodles , Schnauzers; and Terriers.


Very occasionally there may be no signs, but usually affected animals show exercise intolerance  , cyanosis  of visible mucous membranes, fainting (syncope) , and retarded growth rate are seen. A compensatory increase in red blood cells (called polycythemia) is sometimes seen which causes the membranes and tongue to appear very dark - even black.


Auscultation - pulmonic stenosis murmur. Ventricular septal defect murmur.

ECG - changes consistent with right ventricular enlargement * NOTE A Provet video on "ECG Interpretation" is available form the Multimedia Shop GO HERE.

X-rays - Heart size may be normal, or have right-sided enlargement. Small, less radiodense than normal pulmonary blood vessels, and a bulge in the aorta may be seen.

Echocardiography - shows most of the abnormalities

Catheterisation and angiography - shows de-oxygenated blood shunting from the right ventricle into the aorta.


Surgically a subclavian artery can be anastomosed to a pulmonary artery to improve pulmonary perfusion, and oxygenation of blood.

Medical treatment using b -blockers (e.g. propanolol 0.3-1.0mg/kg/tid) may help minimise the secondary hypertrophy by reducing ) workload on the heart.

Low dose aspirin may help reduce the likelihood of thromboembolism due to the polycythemia, and fluid therapy may also be needed to dilute the high packed cell volume (PCV) caused by the polkycythemia - the aim is to keep the PCV below 60%.


Without surgery the prognosis is very poor. Sudden death is common.

Surgery can increase life-expectancy in dogs to 3-4 years


Updated October 2013

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