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Syncope (Fainting) in Dogs

By: PetPlace Veterinarians

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A complete medical history should be obtained and your veterinarian should complete a thorough physical examination with an emphasis on stethoscope examination (auscultation) of the heart and lungs. Medical tests are needed to establish the diagnosis, exclude other diseases, and determine the impact of syncope on your pet. The minimum "database" for syncope varies depending on the duration of signs, presence of systemic signs, and physical examination findings. Recommended tests may include:

  • Exercise test - pre- and post-exercise heart rate and heart rhythm (+/- blood pressure) to determine if routine exercise incites an incident or changes the heart rhythm.

  • Measurement of blood pressure, in order to exclude excessively high pressure that can lead to stroke. The blood pressure is measured with a special device.

  • Blood tests, including a blood glucose, blood biochemical tests, and complete blood count.

  • An electrocardiogram (EKG) is obtained to identify abnormalities in the electrical activity of the heart (arrhythmias). The electrocardiogram is a noninvasive test done by attaching small contact electrodes to the limbs and body. Abnormal rhythms that can cause syncope can be very slow (bradycardias) or fast (tachyarrhythmias).

  • A chest X-ray is needed to identify heart enlargement and fluid accumulation in the lung, and exclude some of the previously mentioned lung and respiratory conditions.

  • Pulse oximetry or tests of blood oxygenation (blood gases) are appropriate if there is evidence of lung disease

  • Heartworm tests should be done in appropriate areas, in pets not taking preventative measures.

  • Additional laboratory (blood) tests, such as those evaluating endocrine (hormone) function, may be needed.

    Your veterinarian may recommend additional diagnostic tests to insure optimal medical care. These are selected on a case-by-case basis (if indicated from the examination, prior test results, or lack of response). When a syncopal patient does not respond to symptomatic therapy or if a definitive diagnosis has not been attained, other diagnostic tests may be recommended. These tests may include:

  • An ultrasound examination of the heart (echocardiogram) can demonstrate diseases of the pericardium, heart muscle, heart valves, and show heart tumors. This test is often a referral examination. This noninvasive test requires sophisticated equipment that creates high frequency sound waves, much like the sonar of a submarine. An image of the heart is created.

  • Some arrhythmias occur very intermittently and may require a prolonged ambulatory EKG (called a Holter monitor) to catch the period of abnormal rhythm. There are also special EKGs called "event" monitors, that can be worn by your pet for weeks. When you observe a spell or faint, you press a button that stores the electrical activity surrounding the event. These tests may require referral to a specialist.

  • Thyroid studies (rare cases of hypothyroidism have severe bradycardia – a slow heart rate – or lead to atherosclerotic disease in the brain).

  • ACTH stimulation studies (to rule out Addison's disease).

  • Blood ammonia or abdominal ultrasound - if laboratory tests suggest hepatic encephalopathy.

  • Plasma immunoreactive insulin (with paired blood glucose) to rule out insulinoma in hypoglycemic patients.

  • Electroencephalogram (after referral if neurologic disease is suspected).

  • Computerized tomography of the brain (after referral, if neurologic disease is suspected).

  • Methemoglobin determination (to diagnose this rare condition).

  • Referral to a specialist for cardiology consultation, neurology consultation and/or internal medicine consultation.


    The treatment for syncope depends entirely on the underlying cause.

  • Therapy for hypotension (low blood pressure) - intravenous (IV) fluids may be indicated, unless the patient has congestive heart failure.

  • Hypoglycemia. Karo syrup can be put on the gums (at home) and intravenous glucose solution can be given in the hospital.

  • Cardiovascular syncope. Arrhythmias may be treated with drugs or, in some cases, a pacemaker.

  • Anemia. Your veterinarian will need to determine the cause and possibly administer a blood transfusion.

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