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Syncope/fainting in dogs: causes, symptoms, and how to react

Author: The DogsPlanet.com Team

Did your dog ever pass out or suddenly faint? This sudden loss of consciousness can be impressive for owners and can have various origins.

In this article, we will explain what syncope is, its causes and treatments.

What is syncope in dogs?

Syncope is a temporary loss of consciousness of the dog. It is characterized by its suddenness and is accompanied by the fall of the dog. The first sign of syncope is therefore a sudden fainting. In some cases, the dog urinates and defecates involuntarily and sometimes vomits.

This loss of consciousness is mainly due to the decreased supply of oxygen and glucose to the brain, due to a decrease in blood flow.

Syncope of the dog: the causes

Several conditions and illnesses can cause your dog to have syncope. Here are the main ones:

Heart problems

This is the set of disorders that cause a lack of oxygen supply to the brain due to a decrease in blood flow. Several conditions lead to a decrease in blood flow, such as the following:

  • Heart rhythm disorders;
  • Pulmonary stenosis;
  • Cardiomyopathy;
  • Cardiac tumor.

Respiratory problems

Syncope can also be caused by respiratory problems that cause breathing difficulties in dogs, some conditions do not provide good oxygenation of the brain due to insufficient oxygen in the blood. Among these respiratory problems are the following:

  • Pulmonary hypertension;
  • Lesions of the pulmonary parenchyma;
  • Airway obstruction (e.g. nostril stenosis).


A drop in blood pressure causes hypovolemia, which is a decrease in the amount of blood in the circulatory system. The blood no longer reaches the brain in sufficient quantity and causes syncope of the dog, in this case we also speak of vagal syncope or vagal malaise. Some of the conditions that cause hypotension include:

  • Severe hemorrhage or dehydration;
  • Ingestion of vasodilator drugs;
  • Intense coughing (especially in brachycephalic breeds such as Pugs or Boxers);
  • Situations of intense exertion or excitement.


Anemia is a decrease in red blood cells and hemoglobin in the blood. The role of hemoglobin is to carry oxygen to various organs including the brain. A decrease in hemoglobin in the blood can cause a decrease in oxygen supply to the brain and may cause syncope in dogs.


Decreased glucose intake to the brain can also cause the dog to faint. Hypoglycemia can have various origins, such as:

  • Metabolic disease: hypocorticism or cirrhosis;
  • Fasting especially in small breeds such as the Poodle;
  • Intense effort on an empty stomach;
  • Heat stroke.

Genetic predispositions

Some dog breeds known as brachycephalic breeds have a morphology that predisposes them to respiratory problems. Indeed, dogs such as the English Bulldog, Beijing or Pug, because of their short and flattened head are prone to respiratory difficulties. It is therefore not surprising to see syncopes more frequently in these breeds.

In addition, some dwarf or small breeds such as the Yorkshire, Dwarf Toy or Dwarf Spitz have a racial predisposition to tracheal collapse. This is a collapse of the trachea that can lead to severe breathing difficulties. These dog breeds are prone to frequent syncope.

Symptoms of syncope in dogs

Before syncope, a few evocative signs may occur even if they are rare and difficult to detect: dizziness and loss of balance due to loss of muscle tone.

The clinical signs of syncope in dogs are:

  • Sudden and temporary loss of consciousness;
  • The dog remains, for a few seconds, lying on its side.

If the syncope lasts, you may observe other symptoms:

  • Seizure;
  • Stiff legs;
  • Involuntary urination and defecation;
  • Vomiting.

It’s important to know that syncope rarely lasts more than a minute. After this episode, the dog usually recovers fairly quickly and gets back on his legs.

If your dog has fainted, it is important to take him to the vet even if he has regained consciousness.

What do I do if my dog has syncope

If your dog has syncope, leave him where he fell if it’s safe to do so. Then place your dog in a lateral safety position to help his breathing. For brachycephalic or similar breeds, prefer the sternal safety position: with the dog on its stomach, back legs bent, and front legs straight.

Don’t wait any longer to go to the veterinarian because, as explained before, syncope can have different causes and only the veterinarian will be able to make a diagnosis and establish a treatment.

Diagnosis and treatment of syncope in dogs

If your dog has had syncope, only the veterinarian will be able to detect the cause. The veterinarian will base his diagnosis on several tests. These may include a total blood workup, x-ray, electrocardiogram, blood pressure measurement and ultrasound.

There is no specific treatment for syncope. The treatment depends essentially on the cause of the discomfort in the dog.


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