Syncope is a sudden, brief loss of consciousness associated with loss of postural tone. Recovery is spontaneous. The mechanism of syncope is poorly understood; as a result, the syndrome is called by many names. Physicians and veterinarians believe that there are many causes of syncope, with the common denominator most likely being stimulation of the medullary vasodepressor region of the brainstem. The end pathophysiologic result is a decrease or brief cessation of cerebral blood flow. It may be difficult to distinguish a seizure from syncope. Episodes of collapse that are precipitated by exercise, stress, micturition, defecation, or pain are more likely to be syncope. If the animal is disoriented and slow to return to consciousness, it is more likely a seizure.

The differential diagnosis of syncope in elderly small-breed dogs requires not only a patient history, but physical examination, thoracic radiographs, electrocardiography, and cardiac ultrasonography. Managing the underlying disorder and minimizing or avoiding precipitating factors are the goals of therapy. If heart failure is present, especially due to advanced mitral valve degeneration, medication may be helpful.

Syncope in small breed dogs. Kraus MS. ACVIM PROCEEDINGS, 2003, p 137.