Dog Fainting: Causes and When it’s an Emergency

If you’ve ever seen your dog faint, you probably already recognize just how scary this can be. Fainting is frightening in any animal (and in humans, too) but it’s upsetting to see your dog suddenly pass out. However, dog fainting is not that uncommon, and there are many potential causes of this symptom as well.

Dog fainting

6 Common Causes of Dog Fainting

In the article below, you’ll find out about six possible causes of fainting in dogs. We’ll also let you know which of these is an emergency, so you can recognize when you need to take your dog to the emergency vet.

Dog fainting can have a variety of different causes, including:

Slow or Fast Heart Rate

Slow heart rate may cause your dog to collapse or faint, especially at times when the heart is trying to work harder than it can. Additionally, a fast heart rate can also lead to fainting under certain circumstances, especially when related to excess activity.

Both of these conditions may be able to be managed or treated through the use of medication. You’ll need to work with your vet to figure out the best way to manage your dog’s heart condition as well as to determine what the underlying cause might be.

Heartworm Disease

Dogs with heartworm disease may faint during the later stages of the disease progression. Heartworm disease causes your dog’s heart to have to work much harder than it should, even for normal everyday activity. Over time, this causes the heart to struggle so much that fainting can occur.

If your dog’s heartworm disease has progressed to the point that she is fainting from it, then there may not be much that can be done to help her. However, you should still work with your vet to try to figure out the best option for your pet.

Certain Medications

Some types of medication can cause a dog to faint. Blood pressure medications, for example, may sometimes lead to your dog’s body responding in the wrong way and can contribute to fainting. If you think medication may be causing your dog’s fainting, talk to your vet, as she may need to be put on a different type of medicine.

Usually, medication shouldn’t cause fainting in dogs as long as it is administered properly and in the correct dosage for your pet. Your vet will give you more information about all of this, and will also let you know of the risks associated with fainting and other severe side effects.

Low Blood Sugar

Low blood sugar can cause dogs to faint, just like it can with humans. If your dog is diabetic or pre-diabetic, or if she simply hasn’t eaten enough in a long time, her blood sugar may drop drastically and may reach dangerous levels.

If this happens to your pet, she may faint or become extremely weak. You should be able to help your dog in mild cases of low blood sugar by simply feeding her the usual food she gets normally. However, if she has fainted from low blood sugar, she will need to go to the vet.


Dehydration can cause fainting when it reaches extreme levels. There are many potential causes of dehydration in dogs, including excessive vomiting and diarrhea. If your dog has been sick or hasn’t had enough to drink, she may suffer from dehydration and may pass out because of it.

If your dog collapses due to dehydration, don’t wait. Take her to the emergency vet right away, as she will likely need IV fluids to help her get back to normal. She may also need to be examined to determine the underlying cause of the dehydration if it isn’t readily apparent.


Finally, heatstroke is an unfortunately common condition that may lead to your dog becoming dehydrated. If your dog is left unattended in a hot car for too long or if she spends too much time being very active on a hot day, she may suffer from heatstroke.

Early symptoms of heatstroke include excessive drooling, excessive panting, and lethargy. As the condition worsens, the symptoms do as well. Dog fainting is one of the final symptoms of heatstroke before death, so if you see your dog faint from heatstroke, get her to the emergency vet as quickly as possible.

Seek Immediate Veterinary Care for Fainting in Dogs

If your dog is fainting without explanation, or if any of the causes on this list seem like they could be accurate for your pet, then it’s time to go to the emergency vet. Don’t wait for your regular vet to be open, as your dog may be suffering from a very severe problem.

The emergency vet will check your pet over and administer any lifesaving treatments necessary. From there, the vet will help you figure out the right treatment for your dog’s condition moving forward, and will also send this information back to your regular vet for future visits.

When it comes to dog fainting, time can truly be of the essence in order to help your pet. With our emergency animal hospital being open 24 hours a day, 7 days a week, you never have to worry about your pet not being able to receive veterinary care. At The Village Vets, your pet’s health is our top priority, and we’ll get to the bottom of what’s causing your dog to faint. For more information about this condition, or if you want to bring your pet in, call us anytime at (404) 371-9774.

Share This Post