Sick Sinus Syndrome - A Heart Condition in Dogs

Sick sinus syndrome has nothing to do with the respiratory system, as one might think. It is a serious cardiac condition that causes abnormal heart rhythms in dogs. It is unclear what is behind the disease, but signs are weakness, fainting, seizures, and even death. There are drugs to help mildly affected patients, but a pacemaker is really the best treatment for symptomatic dogs.


Sick sinus syndrome is a cardiac condition of unknown cause that affects the heart rate and rhythm of both humans and dogs. In this disease, the heart’s electrical impulse-generating sites (called sinuses) fail to function normally. As a result, dogs with this problem are unable to maintain normal heart rhythms, and many also suffer other changes in heart rate.

This disease will vary in severity among dogs, with some suffering catastrophic failure to pump blood (when the heart rhythm is severely disturbed) and others living perfectly normal lives.

For more severely affected dogs, the syndrome can be divided into two classes of patients based on their abnormal heart rhythms: those for whom the rhythm varies from slow to fast (bradycardia-tachycardia) and those in which the rhythm is characterized by slowness and occasional stopping (bradycardia and sinus arrest).

Symptoms and Identification

A low heart rate (or another abnormal rhythm) is the most common finding, but some dogs will be diagnosed only after they’ve collapsed or fainted (known as a syncopal episode) or had a seizure. Episodic weakness is also commonly associated with sick sinus syndrome. Sudden death is always a risk with these patients.

Diagnosing the disease is typically achieved via EKG (ECG or electrocardiogram) and/or a Holter monitor (a device the dog wears for continuous EKG monitoring of the heart rhythm). An echocardiogram (heart ultrasound) is also a necessary step to rule out underlying or concurrent cardiac disease. A trial with a drug that speeds up the heart (atropine) may also be employed in a controlled setting.

Your veterinarian may recommend that you see a veterinary cardiologist for diagnosing or treating this disease.

Affected Breeds

Sick sinus syndrome has been identified in older female Miniature Schnauzers, Dachshunds, Cocker Spaniels, West Highland White Terriers, and Pugs, though other breeds have occasionally been diagnosed with it as well. This disesase rarely occurs in cats.


Some dogs who experience signs of sick sinus syndrome are candidates for treatment. Others may not necessitate any treatment whatsoever. In both cases, it’s a good idea to avoid strenuous exercise and stressful situations. Drug therapy may be employed for mildly affected patients, but a pacemaker is considered best for symptomatic dogs.


Veterinarians do not know the mode of inheritance, and genetic tests are not available. Affected dogs and their parents and siblings should not be bred.

This has been reviewed by a Veterinarian.

Join the Conversation

Like this article? Have a point of view to share? Let us know!