Posted on: March 22, 2022 Posted by: Petsynse Comments: 0

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Greyhound dog passed out on back in dog bed (Caption: Syncope In Dogs)

Syncope is a medical term for fainting or passing out. These fainting spells are usually brief, caused by a temporary loss of oxygen and nutrients to the brain. Most dogs recover spontaneously; however, syncope can be a sign of serious heart problems or other conditions in dogs. We’ll explore what causes syncope in dogs, treatment options, and when to seek help if you think your dog has had a syncopal episode.

Table Of Contents

What Does Syncope Look Like In Dogs?


Syncope (or fainting) is characterized by a temporary loss of consciousness and spontaneous recovery. Syncopal episodes in dogs may occur when they’re sleeping but are more common when they’re excited or exercising. During a fainting episode, your dog may become weak, wobbly, or fall to the floor. Here are some of the signs to look out for during a syncopal episode in dogs:

  • Sudden collapse, falling to the ground
  • Unresponsiveness
  • Weak, floppy limbs
  • Pale gums
  • Urination or defecation
  • Involuntary muscle twitching

Some dogs cough and fall over before fainting, whereas other dogs throw up before passing out. Here’s a video showing what a syncopal episode looks like.

Syncope vs Seizures

Syncope can sometimes be confused with seizures in dogs. In general, seizures occur at rest rather than during exercise and last longer than a syncopal episode. Seizures may be accompanied by a loss of consciousness or vacant episode before and after the event and are characterized by stiff, rigid muscles and more extreme muscle tremors or shaking.

Dogs usually recover faster from a syncopal episode and are back to normal in a few seconds. However, both conditions have similarities, and it can be difficult to distinguish between them. If you’re concerned that your dog has had a syncopal episode or a seizure, then seek immediate veterinary attention.

Causes Of Syncope In Dogs

Syncope is caused by a reduced blood supply to the brain that temporarily starves the brain cells of oxygen. A dog fainting or collapsing when excited or exercising is not normal, and this can be a sign of an underlying health problem. Let’s explore some of the causes for syncope in dogs:

Heart Disease

Dog on back doing CPR

Heart-related syncope in dogs results in low blood pressure with temporarily reduced blood flow to the brain. As a result, the dog’s brain goes ‘offline’ or loses consciousness momentarily. Low blood pressure can be caused by the heart beating too fast or too slow or with an irregular rhythm. Narrowing, or leaking of the heart valves (e.g., mitral valve disease) can also reduce the flow of blood out of the heart.

Some dogs are born with structural problems of the heart (congenital heart disease). And in some dogs, the heart can change in shape or function later in life (e.g., cardiomyopathies such as dilated cardiomyopathy or hypertrophic cardiomyopathy). Some breeds are more prone to developing heart disease and fainting, including, Miniature Schnauzers, West Highland White Terriers, Boxers, and Dobermans.

Breathing Problems

Diseases of the lungs or breathing problems that result in less oxygen being passed around your dog’s body can result in fainting. Dogs that have a short nose and airway, also known as brachycephalic dogs (e.g., Bulldogs, Pugs, and Boxers), are more likely to faint if they exert themselves physically — the shape of the airway means they cannot get enough oxygen in when they breathe. If your dog coughs and falls over, she may be suffering from a syncopal episode.

Metabolic Disease

Diseases that change the chemistry within your dog’s blood can affect nutrient supply to the brain. A common example would be low blood sugar (hypoglycemia). A syncopal episode is unlikely to occur just because your dog has skipped breakfast. However, if your dog is frequently having episodes of low blood glucose that results in fainting, it could indicate a problem with her blood sugar control, such as diabetes or diseases related to the insulin hormone. Changes in calcium (hypocalcemia) or sodium levels (hyponatremia) in the blood secondary to other hormone diseases can also cause fainting episodes.

Vasovagal Syncope In Dogs

The vagus nerve helps to regulate blood pressure in the body and to slow the heart rate down. During heightened emotional stress or excitement, the nervous system may cause the heart to beat very quickly and result in high blood pressure. The vagus nerve may respond by temporarily dropping blood pressure. If blood pressure falls too low, then the flow of oxygenated blood to the brain decreases, and your dog may faint. Sometimes, pressure on the vagus nerve caused by deep coughing, vomiting, or abdominal pressure can press on the vagus nerve and cause vasovagal syncope in dogs.

Bleeding Disorders

Bleeding or blood clots in the body can reduce blood pressure and result in syncope. Blood clots in the heart chambers or lungs (also called thrombi or thromboemboli) can interfere with blood flow out of the heart and to the brain. Severe, internal bleeding from major organs such as the spleen or liver will reduce blood pressure within the body and may result in fainting or collapse if blood flow to the brain cannot be maintained. These can be serious, life-threatening causes of collapse in dogs and require urgent veterinary care.


Golden dog taking pill from owner's hand

Many medications affect blood pressure. It’s important to follow the dosage instructions carefully on any prescribed medication for your dog and never administer medication to your dog without consulting with a veterinarian first. If you’re concerned that your dog has fainted due to the medication she’s been prescribed, then seek veterinary advice before stopping the medication suddenly.

Carotid Sinus Pressure

The carotid vessels sit on either side of your dog’s neck and deliver oxygenated blood to the brain. Pressure on these vessels caused by excessive pressure on a dog’s lead or collar could result in syncope.

How Is Syncope In Dogs Diagnosed?

Beagle laying on side at vet

While most dogs recover quickly from syncopal episodes once blood flow to the brain is restored, diagnosing the cause is important for your dog to get the correct treatment. Your dog’s veterinarian will take a detailed history about what the syncopal episodes look like and when they occur and perform a physical examination. Additional tests such as blood tests to assess your dog’s red blood cell level, blood glucose levels, and blood chemistry may be needed.

If your veterinarian suspects heart or lung problems, they may perform tests to assess the structure of the heart such as ultrasound (echocardiography) or an ECG (electrocardiogram) to monitor the rhythm of your dog’s heart. Some dogs may even need to wear an ECG for 24 hours, called a halter monitor, while they go about their normal routine to detect intermittent changes to heart rhythm. If your veterinarian suspects a bleeding problem or a problem with the internal organs could be responsible for fainting episodes, then scans or x-rays may be necessary.

How Do You Treat Syncope In Dogs?

Treatment of syncope depends on the underlying cause. Many of the diseases that result in syncope can be managed or even reversed with the correct treatment. In specific cases, drug treatment may be available to minimize the problem. Some heart diseases may even require a surgical procedure, for example, fitting a pacemaker, to reduce the problem. Don’t delay in seeking veterinary advice if you’re concerned your dog has had a syncopal episode.

Home Care For Syncope In Dogs

Most dogs will regain consciousness soon after fainting, but what can you do to help if your dog passes out when excited or is exerted? If your dog faints or collapses, keep her cool and calm. Heat stress can contribute to syncope, so move them out of direct heat to a cool, shaded area.

Allow her to calm down and her heart rate to return to normal, avoiding any further excitement or exertion. If you’re out walking with your dog when this occurs, try to find an alternative way home rather than continuing with the walk.


The good news is that many fainting episodes are not linked to serious underlying diseases, and the frequency and severity of syncope can be reduced with careful management. Syncope episodes are not considered painful or distressing to your dog, and most will recover quickly from the event.

The biggest concern is to rule out any serious underlying disease that may be a threat to your pet. Heart-related syncope in dogs may be associated with a worse prognosis or require long-term treatment and management.

What Else Can Cause Dogs To Collapse?

If your dog’s collapse symptoms don’t appear to be syncope, some other conditions can cause dogs to become weak and collapse, including heat stroke and some types of seizures, as we mentioned above. There’s also a genetic condition called Exercise-Induced Collapse (EIC), which is an inherited neuromuscular disease. With EIC, an otherwise healthy and fit dog will become weak, and her hindquarters will collapse after 5 to 15 minutes of strenuous exercise.

Any time your dog collapses with an unknown cause, it’s crucial to seek veterinary treatment immediately to determine the cause and get proper treatment.

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