Health Topics  >  Musculoskeletal  > Collapse or Fainting

What causes collapse in dogs?

There are numerous causes of collapse in dogs. Describing the particular way your dog has collapsed, what they were doing when it happened, and how they behaved afterwards, can aid your veterinarian in making a diagnosis. Some common causes of collapse include:

Heat Stroke

Heat stroke is one of the more obvious causes of collapse; if your dog collapses while exposed to extreme temperatures, you can usually assume that overheating is the culprit.

Dogs don’t need to be actively exercising to experience heat stroke. In fact, certain predisposed breeds like Bulldogs and Pugs may experience heat stroke just lying out in the sun or attempting a leisurely walk. Another common cause is being left in a hot car (on hot days, a cracked window will not be enough).

Heat stroke is an entirely preventable condition, so always keep your dog in well ventilated areas with access to shade and water. Treatment typically involves cooling your pet in a controlled manner, as well as IV fluid support and oxygen therapy.

Heat stroke or hypothermia is one of the most common causes of collapse, but an entirely preventable condition. Always keep your dog in well ventilated areas with access to shade and water.

Heart Disease

One of the most common causes of fainting (known medically as syncope) is an underlying heart condition. An irregular heart rhythm (arrhythmia) can cause a brief disruption in blood flow to the brain. Dogs with an arrhythmia may or may not have a diagnosed heart disease at the time of their first episode.

Often they are walking or running when they suddenly drop to the ground. Tragically, in rare cases an arrhythmia can cause sudden death. In most cases however, the fainting episode is brief and they regain consciousness in moments. 

Dogs with congestive heart failure (CHF) can also collapse if they are not able to oxygenate their lungs well. Usually this is not a sudden collapse, but instead  a gradual onset of laboured breathing over days to weeks. One morning their breathing may be labored enough to the point that they just don’t have the energy to get up  and walk.

Respiratory Diseases

Any dog who is having difficulty breathing is at risk of collapse if their oxygen levels drop too low. Most commonly, we see this happen to dogs with ‘squished noses’ (such as French Bulldogs, Boston Terriers and Pugs), otherwise known as brachycephalic airway syndrome. On hot days especially, when their tissues become swollen, they can struggle to breathe leading to collapse. 

Other airway conditions known to lead to collapse are collapsing trachea (when the cartilage in the trachea collapses, air cannot easily get to the lungs) in small breeds such as Pomeranians, and laryngeal paralysis (when the laryngeal muscles weaken, it is difficult to move air to the lungs) in large old dogs like Labradors.

Respiratory causes of collapse are treated with sedation and oxygen therapy, usually via an endotracheal tube. Without surgical correction of the underlying issue, however, dogs are prone to having a recurrence of these episodes. 

Brachycephalic airway syndrome is most commonly seen with ‘smushed face’ dogs with shorter snouts like French Bulldogs and Pugs.


While not terribly common, severe allergic reactions (anaphylaxis) can cause a dog to collapse due to a sudden drop in blood pressure. The most common cause of severe anaphylactic reactions in dogs would be allergy to a vaccination, or a bee sting. Again, reactions like this are exceedingly rare.

If your dog has a known history of vaccine reactions, always make sure your veterinary clinic is aware of this. Certain vaccinations may need to be avoided or pre-medications may be administered prior to future vaccinations.

Internal Bleeding

Internal bleeding (most often into the abdominal cavity) is an unfortunately common cause of collapse in older large breed dogs. The most common culprit is a bleeding tumor on the spleen, liver, or heart. While the tumors themselves can be slow growing, a sudden rupture can lead to blood loss, weakness, and collapse. In these cases, other symptoms may include:

  • Pale pink or white looking gums
  • A rapid heart rate
  • Possibly a distended looking belly


Diagnosis of this condition is made most definitively by ultrasound, though blood tests and x-rays help to get the whole picture. Emergency surgery is generally the only way to stop the bleeding, and even when this is done promptly, long term prognosis is usually poor. Therefore, preventative wellness exams and early diagnosis is key in these cases.

Another cause of internal bleeding more commonly seen in young dogs would be ingestion of an anticoagulant poison (ie: rat poison). These cases are diagnosed based on history, blood tests, and by ruling out other causes of bleeding. 

Seizure Activity

Seizure activity can typically be distinguished from other types of collapse by the average pet owner. The most common form of seizures in dogs appears to start out as collapse followed by muscle stiffening and a cycle of muscle contractions, known as a tonic/clonic cycle (see a video example here).

Dogs with seizures will often urinate or defecate during an episode. Most seizures last from 30 seconds to a couple of minutes. The longer they go on (and the more frequent they are), the more risk they pose to your dog.

Hypoadrenocorticism or Addison’s Disease

Hypoadrenocorticism (also known as Addison’s Disease) typically affects young dogs and can present with a number of vague symptoms. Signs include waxing and waning vomiting and diarrhea, lethargy, trembling, and in the most serious cases, collapse.

Addison’s Disease is diagnosed via blood tests. Treatment involves fluid therapy and steroid treatment. Long term medical management generally has a great prognosis.


Extremely low blood sugar can cause seizures in dogs. This can occur in young puppies who are malnourished or vomiting and have diarrhea. It can also occur in diabetic pets who have accidentally been overdosed with insulin.

Another cause is a rare type of tumor called an insulinoma. Your veterinarian will often start by checking blood sugar levels in a collapsed pet.

Arthritis or Other Musculoskeletal Issues

Older dogs with chronic joint disease (osteoarthritis) may at some point collapse or be unable to rise when the pain or weakness reaches a critical point. This sort of collapse is usually preceded by many months or years of stiffness and discomfort. Bilateral cruciate ligament tears can also cause collapse, but are considered fairly rare. 

Spinal Cord Disease

Conditions that impinge or inflame the spinal cord can lead to collapse in the affected limbs. Most commonly, dogs will collapse in the hindlimbs only, but in some cases all four limbs, or one side of the body becomes paralized.

Examples of this condition include Fibrocartilaginous Embolism (FCE) in large breed dogs, Intervertebral Disc Disease (IVDD) in small breed, long-backed dogs (ex. Daschunds), and Degenerative Myelopathy (DM) in older large breed dogs, especially German Shepherds.

Toxin Ingestion

The most common toxins to cause collapse in dogs include:

  • Xylitol: artificial sweetener found in some sugar-free gums. This can lead to a sudden drop in blood sugar
  • Rat Poison: anticoagulant rat poison can cause internal bleeding which in some cases leads to collapse
  • Marijuana: More commonly associated with a staggering gain and inappropriate urination, marijuana ingestion can cause some dogs to collapse

Pro Tip: If you suspect your dog has ingested a toxin or poison, you can call the ASPCA Pet Poison Control (available 24/7).