Atrial fibrillation

Veterinary advice should be sought before applying any treatment or vaccine.

Atrial Fibrillation

Atrial fibrillation (AF) is one of the most common types of arrhythmia (irregular heart beat) in horses. It is caused by a distortion of electrical messages that control the steady rhythm of the horse's heart, known as the 'heartbeat'. Equine arrhythmia are associated with poor performance in horses. AF can present as acute or chronic condition in horses. AF is essentially a rapid atrial rate and a slower ventricular rate, due to the blocked rapid atrial impulses in the AV node that aren't able to enter the ventricles. When AF occurs, the upper chambers of the heart quiver rapidly and irregularly.

There is speculation that electrolyte abnormalities might be associated with the development of AF in horses. Horses suspected of AF should be evaluated for the possibility of an electrolyte imbalance, and treated if necessary. Older horses with AF often show signs of congestive heart failure, prominent murmurs, and a rapid resting heart rate.


Exercise intolerance
Increased heart rate during exercise
Nasal discharge
Shortness of breath


  • History
  • Clinical signs
  • Physical exam
  • Blood tests
  • Electrocardiogram
  • Echocardiogram


QuinidineAdministered as quinidine sulfate via nasogastric intubation or quinidine gluconate administered IV. Treatment with quinidine sulfate is associated with a 70 to 89% success rate in horses with AF.
DigoxinAdministered concurrently with quinidine sulfate
Transvenous electrical cardioversion (TVEC)Reported to have a 94-99% success rate
No treatmentSome horses may not require any treatment.


  • Ensure horses does not get dehydrated, as dehydration predisposes horses to developing abnormalities of acid base and electrolyte abnormalities.


The prognosis of the horse depends on the presence of underlying cardiac disease, however even when successfully treated, recurrence occurs frequently.

Scientific Research References

Good Overviews

Risk Factors

  • Breed - Standardbreds, Warmbloods, and Draft horses are at a greater risk of developing AF than other breeds of horses.