Horse Side Vet Guide ®

Equine Health Resource

Syncope (Fainting)

Synonyms: Vaso-Vagal Syncope

Fainting (Vaso-Vagal Syncope) is relatively common in people, and is associated with fear or emotional shock. Fainting is thought to involve an inappropriate, automatic nerve/blood pressure response when presented with a fight/flight situation. Instead of blood pressure increasing as it should, it actually decreases. If the decrease is sufficient, the brain momentarily does not get adequate blood flow and the person collapses. Once down, gravity favors better brain blood flow, the situation auto-corrects and the person regains their feet.

In horses, this mechanism has never been proven and it is unclear whether this condition really exists. Horse may appear to “faint” and fall to the ground due to poor blood flow for various reasons including low blood sugar or seizures. Rarely, otherwise healthy horses that are excited by a sudden event spontaneously collapse and then later rise. Based on these rare occurrences, vets assume that a mechanism similar to what occurs in humans may occur in horses.

Diagnosis is usually made by ruling-out other possible causes, especially heart-related conditions.

Treatment depends on the specific case, and the treatment of the underlying conditions.


  • What is the underlying cause?
  • What can be done to minimize the likelihood of this recurring?
  • What is the risk in riding this horse?
  • Have all the other possible causes been ruled out?

    In horses that collapse when girthed or cinched up, cinch the horse incrementally. A professional should evaluate saddle and girth fit.

    If collapse has occurred in response to sudden increase in work or exercise, be sure the horse is adequately warmed up, and the heart rate allowed to rise more gradually.

    Be very cautious about riding a horse that has repeatedly collapsed, and for which there is no diagnosis and no treatment plan.

    Author: Doug Thal DVM Dipl. ABVP


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