Horse Side Vet Guide ®

Equine Health Resource

Collapsed & Died Suddenly, Witnessed

Code Red - Call Your Vet Immediately, Even Outside Business Hours

Code Red - Call Your Vet Immediately, Even Outside Business Hours

  • A post-mortem exam (necropsy) may help to identify the cause of death.

Your seemingly well horse has just mysteriously and suddenly collapsed and died in front of you, or worse yet, while you were mounted. Sudden death usually (but not always) follows strenuous exercise of some kind. What happened and what should you do now?

Ruptured aortic aneurysm is one of the most common causes during or immediately following intense exercise. It is more common in stallions. Sadly, in rare cases, winning competitors have fallen over dead from this condition, immediately after brilliant performance. Collapse and death usually follows rupture of an aortic aneurysm within a few moments. Severe internal bleeding from any ruptured great vessel can cause sudden collapse and death.

There are other causes too. Stroke (vessel accident in the brain) may occur in horses, but is poorly understood and difficult to diagnose. It can result in collapse but rarely rapid death. Horses that receive an attempted intravenous injection into the carotid artery will often collapse, and can die. Traumatic injuries that involve brain or spinal cord can kill a horse almost instantly but are usually associated with a severe and obvious accident. Heart attacks, common in people, are considered to be very rare in the horse.


I recommend that you immediately contact your vet to perform a post-mortem examination to determine the cause of death. Although the possibility is remote, your first concern should be your own safety (transmissible disease) and that of other horses (contagious disease). Understand that internal hemorrhage from a ruptured aneurysm is the most common cause of sudden collapse and death, but not the only one.


A necropsy (post-mortem exam) is best performed within a few hours of death. Examination will focus on the body systems likely to be associated with sudden collapse and death – the cardiovascular and nervous system. In rare cases, a diagnosis cannot be made even with a thorough post-mortem exam and laboratory diagnostics.

Author: Doug Thal DVM Dipl. ABVP


We're not around right now. But you can send us an email and we'll get back to you, asap.