Syncope in Dogs: Diagnosis, Treatment, and Recovery

Syncope in dogs occurs because of a sudden decrease in blood or oxygen to the brain.  

This causes a dog to lose consciousness, become limp, and collapse. These episodes are generally brief, with dogs recovering on their own, but determining the underlying cause is essential.  

What Is Syncope in Dogs?

Syncope in dogs occurs because of a sudden decrease in blood or oxygen to the brain.  

This causes a dog to lose consciousness, become limp, and collapse. These episodes are generally brief, with dogs recovering on their own, but determining the underlying cause is essential.  

If your dog has fainted but then quickly recovers, call your veterinarian promptly and they will try to identify the underlying cause.  

If your dog has fainted and isn’t recovering, take them to an emergency veterinarian immediately.  

Symptoms of Syncope in Dogs

Symptoms of syncope in dogs include:  

• Collapse  

• Loss of muscle tone 

• Involuntary urination or defecation 

• Vocalizations, such as whimpering 

• Pale gums 

Causes of Syncope in Dogs

Syncope can affect dogs of any age, but it’s more common in senior dogs and young dogs with congenital heart defects.   

Brachycephalic breeds, such as Boston Terriers and Pugs, are more likely to experience syncope due to the anatomy of their airways.  

Exercise and excitement can further obstruct air flow and reduce oxygen to the brain.  

Dogs predisposed to heart disease, such as the Doberman Pinscher and the Cavalier King Charles Spaniel, have an increased risk for syncope as well.  

The main causes of syncope involve conditions that interfere with the delivery of blood and oxygen to the brain.  

Let’s look at these causes and how they can cause fainting: 

• Heart disease. Heart disease is the most common cause of syncope, because without normal pumping ability to maintain blood pressure, adequate blood and oxygen can’t reach the brain. Conditions such as pericardial effusion, arrhythmias, and congenital shunts can lead to syncope.  

• Airway disease. Airway diseases, such as pneumonia and pulmonary hypertension, can reduce oxygen in the blood and force the heart to work harder. As a result, a lack of oxygen and reduced blood pressure can lead to fainting.  

• Hypoglycemia. Dogs with low blood sugar can faint because their brains don’t receive enough glucose. Hypoglycemia can be caused by underlying liver disease, cancer, Addison’s disease, or toxin ingestion. 

• Vasovagal response. Straining while defecating, intense coughing, excitement, or strenuous exercise can trigger a dog’s nervous system to overreact and abruptly lower blood pressure, causing fainting.  

• Blood loss. Blood loss can lead to anemia, a condition where the blood can’t carry enough oxygen to the brain. Parasites, traumatic injuries, and toxin ingestion can cause blood loss and subsequent fainting.  

• Medication use. Medications prescribed to lower blood pressure, such as amlodipine, may inadvertently cause blood pressure to drop too low, resulting in fainting.  

How Veterinarians Diagnose Syncope in Dogs

Your veterinarian will diagnose syncope based on a thorough history, a physical exam, and diagnostic testing.  

To start, provide them with as much information as you can about the fainting episode, including what happened before, how long it lasted, and your dog’s behavior directly afterward.  

During the exam, your vet will check your dog from head to toe for any obvious abnormalities. They will listen closely to your dog’s heart and lungs to identify any murmurs, arrhythmias, or abnormal breathing patterns.  

Your vet may also recommend diagnostic testing, such as:   

• Blood work: A small sample of blood from your dog’s vein can be used to check their overall health, including blood cell counts and organ function, and to rule out heartworm disease. 

• Urinalysis: A urine sample can help assess your dog’s overall health and diagnose non-cardiac diseases that could cause fainting.  

• Imaging: An X-ray of your dog’s chest can show airway abnormalities or heart enlargement that may indicate underlying disease.  

• Blood pressure: Because syncope is linked to low blood pressure, checking this vital sign is important to detect low readings.   

• Electrocardiogram (ECG/EKG): This non-invasive test uses sensors attached to your dog’s skin to record their heart’s electrical activity. If this test is abnormal, a referral to a cardiologist for more specialized testing, such as an echocardiogram, may be necessary.  

Treatment of Syncope in Dogs

Treatment of syncope in dogs focuses on the underlying cause for the syncopal episodes.  

Syncope can be cured in some cases, such as if it resulted from blood loss, low blood sugar, or a specific medication.  

Correcting the blood volume or sugar levels and discontinuing the problematic medication would be effective treatment for these dogs. 

However, if the fainting episode occurred due to a heart or airway disease, these conditions likely can’t be cured but can be managed to prevent future episodes.  

Potential treatments that a veterinarian may recommend include:  

• Cough suppressants, such as hydrocodone 

• ACE inhibitors, such as enalapril, to regulate blood pressure 

• Antiarrhythmics, such as diltiazem, to treat arrhythmias 

• Diuretics, such as furosemide, to remove fluid buildup in the lungs or abdomen 

• Antibiotics, such as Clavamox, to treat bacterial lung infections 

• Sildenafil to treat high blood pressure in the lungs 

• Vetmedin to help the heart pump efficiently 

• A pacemaker to regulate the heart rate 

• Blood transfusions to restore blood volume 

• Fluid therapy to correct electrolyte levels, glucose, and blood pressure 

• Airway surgery, especially in brachycephalic breeds, to relieve breathing difficulties 

If a dog is having frequent syncopal episodes or severe symptoms of underlying disease, hospitalization and supportive care with oxygen therapy is necessary.  

Recovery and Management of Syncope in Dogs

Recovery typically occurs in seconds or minutes—as soon as enough oxygen returns to the brain.  

While a syncopal episode is concerning to witness, most dogs recover quickly and act like nothing happened.  

However, the underlying condition causing syncope can be serious or even life-threatening. If your dog experiences a fainting episode, they should always be evaluated by a veterinarian as soon as possible to determine the underlying cause.  

Prevention of Syncope in Dogs

You can take the following steps to reduce your dog’s risk of syncope:  

• Ensure your dog stays up to date on veterinary check-ups to identify and treat health issues as early as possible.  

• Manage any underlying health conditions that could contribute to syncope by following your veterinarian’s instructions closely.  

• Keep your dog at an optimal weight by feeding a high-quality diet, such as Hill’s Science Diet Perfect Weight Management, to reduce the heart’s workload. Ensure they always have access to fresh clean water. 

• If your dog has been diagnosed with tracheal collapse, use a harness instead of a collar to avoid putting pressure on their airway. 

• If your dog has heart disease or brachycephalic airway syndrome, restrict their exercise, especially in hot weather.  

• Support a calm, stress-free environment through predictable routines, mental enrichment, and cozy bedding.