Fainting on the dog is not usually serious, but we can block ourselves with fright and not know what to do. Find out what canine syncope is, why it occurs and how to act if it happens to your pet.

The s íncope canine is a sudden loss of consciousness, acute, transient, and reversible. Colloquially, it is synonymous with fainting in the dog or lipothymia. 

The mechanism that leads to syncope is the shortage of oxygen or glucose in the dog’s brain for various reasons. It is an organ that needs a constant and sufficient source of oxygen and glucose to develop its functions normally and maintain the animal’s consciousness and alertness.

Causes of syncope in dogs

Any cause leading to a lack of oxygen or glucose in the dog’s brain can trigger fainting. The most common causes of canine syncope are:


The blood glucose level is too low, and not enough supply reaches the brain. It occurs in hypoadrenocorticism, in dogs with diabetes in which too much insulin has been injected, and in small breed dogs, puppies, or athletes, who consume glucose very quickly.

Heart problems

Dilated cardiomyopathy or arrhythmias cause not enough blood to be pumped to the brain, complicating oxygen delivery.

Respiratory problems

Restrictive diseases, such as pulmonary fibrosis or tracheal collapse, and an episode of dyspnea or respiratory distress, can restrict oxygen delivery to the blood, especially after intense exercise, at high temperatures, or in the event of drowning the pet.


The decrease in the haemoglobin concentration in the red blood cells prevents sufficient oxygen in the blood from being transported to the brain.


When the pressure in the blood vessels drops, there is not enough blood flow to the brain, and the necessary oxygen and glucose do not reach easily. It can occur after an episode of fear, stress or pain, vomiting, diarrhoea or severe cough, or after injecting medication. This type of syncope is called vasovagal.

Predisposing factors for canine fainting

Syncope can occur in dogs of any breed, sex, and age. However, brachycephalic breeds are predisposed to suffer from it due to the respiratory distress that many suffer from, and small breeds and puppies tend to have hypoglycemia. Due to their metabolism, they expend energy from glucose very fast.

syncope in dogs

Symptoms and diagnosis of syncope in the dog

If you want to identify whether your dog is giving a faint note that usually does not show symptoms earlier, but in the s íncope canine, a sudden occurs loss of consciousness in which the dog loses muscle tone, falling to the ground with flaccid limbs, for less than a minute.

Some dogs show signs of syncope such as pale mucous membranes, minor spasms, or stiffness in the limbs and neck, and, very rarely, they vomit, urinate, or defecate. In most cases, dogs regain ordinary consciousness and posture spontaneously, quickly, and ultimately, without residual sequelae or symptoms.

Differences between canine syncope and a seizure

There are usually previous signs before an attack in dog seizures, but not in syncope, which occurs without warning. During an episode, dogs generally show intermittent contraction and relaxation of the limbs, making sudden movements. It is more common to observe excess salivary secretion or spontaneous urination and defecation.

In addition, at the end of the attack, they usually wake up in a daze, but after a canine syncope, recovery is immediate and complete. However, if in doubt, it is better not to wait and immediately call the emergency vet, who will tell us how to act.

Diagnosis of syncope in the dog

In these cases, the essential thing is to confirm that it is syncope and find out if there is an underlying disease causing it, such as heart disease or metabolic disease, to treat it and prevent further fainting. To do this, the vet will measure blood pressure, perform an electrocardiogram to look for arrhythmias, and chest x-rays and echocardiography to assess the shape and functionality of your pet’s heart. In addition, you may need blood and urine tests to check glucose or cortisol levels.

Some data that are useful in the diagnosis of syncope in the dog are, for example: if the dog has fainted before, when did it occur, if it turns pale or bluish, what the dog was doing before the syncope ( intense exercise, coughing, urinating, vomiting or defecating), if you were in a hot place, if you had access to objects with which you could choke if you have a previous illness, and if you take any medication on a regular or regular basis.