Syncope (Fainting) In Dogs

Michael Kearley, DVM
By Michael Kearley, DVM on Mar. 3, 2023

In This Article


What Is Syncope in Dogs?

Syncope is the medical term for fainting, which can occur both in dogs (and cats), due to a lack of oxygen or nutrients to the brain. Syncope in dogs is considered a medical emergency—immediate treatment is urgent and critical.

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Symptoms of Syncope in Dogs

The most obvious symptom is acute collapse of your dog, often with stiff limbs and body. Your dog may lean or stagger at first and then fall to one side. Urination and (rarely) defecation may occur concurrently with the fall. Other symptoms, which are also useful in arriving at a diagnosis, may include an underlying heart murmur or arrhythmia. 

Not all dogs that suffer from this condition will require treatment, but all are usually put through a series of tests to arrive at a diagnosis. Syncope is considered to be more of a clinical sign than a disease, and occurs when there is a sudden loss of consciousness associated with the collapse of the dog. It is temporary, and dogs usually recover after only a few seconds to minutes.

What Is the Difference Between a Seizure and Syncope?

It can be very challenging to differentiate a seizing dog from one that has only fainted. Even trained personnel can have difficulty distinguishing the two, and a video recording of the event can certainly be helpful in narrowing down the possibilities. You will probably be asked by the veterinary staff to describe the event in as much detail as possible, including any events leading up to the episode and afterward.

The following often occurs with syncopal episodes:

  • The episode itself lasts for a short duration.

  • It is usually preceded by an event, such as coughing or some sort of excitement.

  • Most often the dog has a rapid recovery.

  • The dog may have an underlying disease such as a heart murmur or arrythmia.

A seizure occurs due to abnormal brain activity; it is the sudden, uncontrollable, and uncoordinated movement of the body. Dogs typically are witnessed with:

  • Pre-ictal phase, noticed as pacing, whining, or generally acting “weird”

  • Twitching movements, especially of the face

  • A longer time to recover, followed by disorientation or weakness

  • Defecation, urination, and even salivation, possibly simultaneously

  • An neurologic condition or neurologic deficits after the seizure

Causes of Syncope in Dogs

Multiple conditions and underlying diseases can cause fainting in dogs:

  • Cardiovascular conditions including arrhythmias, heart failure, dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), mitral valve disease, pericardial effusion, pulmonary hypertension, and congenital heart defects. Other conditions such as cancer or diseases that affect blood output (e.g., heartworm disease) can have similar effects.

  • Neurologic conditions including brain tumors, vascular disease, and narcolepsy

  • Acute hemorrhage (blood loss) or profound anemia (low red blood cell count)

  • Hypoglycemia (low blood sugar)­ or electrolyte abnormalities

  • Adverse or known drug side effects, from drugs such as vasodilators or beta blockers

  • Situational syncope, often due to a sudden change in pressure within the body from an event such as coughing, vomiting, urination, or defecation. Pulling tightly on a dog’s collar or leash can have similar effects, though due to a different mechanism.

  • Vasovagal syncope, due to a sudden drop in blood pressure often preceded by some sort of stressful or emotional situation that causes a change in body reflexes

How Veterinarians Diagnose Syncope in Dogs

Your dog’s clinical history and physical exam can often not only facilitate a diagnosis of syncope but also provide insight into an underlying cause as well as a way forward for possible treatment options. It’s always helpful if you can provide a detailed account of the event itself, as well as what occurred before and after the event.

Bloodwork and urine testing will most likely be recommended, as well as a heart work-up including chest X-rays, EKG (a 24-hour Holter monitor may be needed for the diagnosis of arrhythmias), blood pressure, and echocardiogram. Referral to a veterinary cardiologist or neurologist to consider neurologic conditions with a test such as CT, MRI, or CSF tap may also be discussed and recommended.

Treatment for Syncope in Dogs

The prognosis is variable and often related to the underlying cause. For dogs suffering from situational syncope, limiting or preventing provoking situations is key. For instance, if syncopal events occur every time your dog becomes excited when the doorbell rings, then disconnecting the doorbell or installing another system may be the appropriate fix. Switching to a harness instead of a collar or leash is also advisable.

Treatment for dogs suffering from a heart condition will also vary. Arrhythmias or heart failure will often benefit from medications such as sotalol, an anti-arrhythmic, or enalapril, which helps regulate blood pressure. Surgical procedures may be warranted for dogs requiring a pacemaker or in cases of a blockage or tumor, or when needed to resolve pericardial effusion. Chemotherapy or radiation may be necessary to treat cancer.

Dogs showing electrolyte abnormalities or low blood sugar may require IV fluids and supplementation. Blood loss will require a transfusion. Discontinuing medications that could be causing a condition may also be recommended. 

Recovery and Management of Syncope in Dogs

It is important to partner with your veterinarian to determine the underlying cause and to prevent or minimize the chances of future fainting spells from occurring.

Avoiding known triggers, such as excitement caused by the mail carrier or the doorbell ringing, and limiting your dog’s physical activity are crucial. If your dog is prone to syncope, “dog-proofing” your home is advised. For instance, using gates to block access to the stairs or pool, and using corner protectors for furniture in addition to having padded surfaces like rugs or carpet, can cause less harm to your dog if they faint.

If your dog is prescribed medication, chances are they will be needed for life so never stop medication suddenly or without direction from your veterinarian. It is also important to attend any future follow-up appointments, as monitoring the response to prescribed medications or periodic placement of a Holter to monitor for persistent arrhythmias will prove invaluable to a speedy recovery, resulting in better quality of life.  

Syncope in Dogs FAQs

What does fainting look like in dogs?

Typically, the dog will fall over with stiff legs and rigid body; urination and (rarely) defecation may occur at the same time as well. After a few moments, the dog will get up and continue as normal. 

What do I do if my dog faints?

The first thing is to remain calm. Be sure your dog is not in danger of harming himself or you in the process. He should recover momentarily, and you should immediately seek veterinary attention. 

Featured Image:

Michael Kearley, DVM


Michael Kearley, DVM


Dr. Michael Kearley graduated from the University of Florida College of Veterinary Medicine in 2013. He graduated with a certificate in...

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