A heart arrhythmia, or irregular heartbeat, is a performance-limiting condition commonly seen in athletic horses. While some arrhythmias are benign, others may indicate cardiac disease or another underlying health condition.

The horse is a supreme athlete with a powerful heart that can beat up to 250 times per minute during strenuous exercise. Performance horses need to pump large volumes of blood throughout the body and maintain an elevated heart rate for a extended periods during competitions and training.

With regular conditioning, the cardiovascular system adapts to support improved athletic ability. [1][2] Intense training regimes produce structural changes in the heart, including increased cardiac mass. However, repeated exertion can also increase the susceptibility of horses to developing arrhythmias.

Horses affected by an irregular heartbeat may experience reduced stamina, increased fatigue, and an increased likelihood of developing severe heart conditions or experiencing sudden cardiac events.

Arrhythmias in performance horses can also be triggered by electrolyte imbalances, dehydration, agitation, or can occur secondary to another infection or medical condition. Even though many arrhythmias are harmless, they should always be investigated to rule out heart disease.

Arrhythmias in Performance Horses

Cardiac arrhythmia is a common condition, with 25% of horses having arrhythmias that can be detected during veterinary examination. [3] While some arrhythmias limit performance, they often go undetected and unnoticed. [4]

Many benign arrhythmias appear spontaneously without cause and do not impact the horse’s quality of life. These do not require treatment.

Other arrhythmias develop secondary to an underlying condition, such as: [3]

  • Heart disease
  • Congenital defects
  • Metabolic disorders (EMS, PPID, etc.)
  • Systemic inflammation
  • Fever
  • Anemia
  • Toxicosis or medication use

Clinical Signs

Presenting signs for arrhythmias in horses are highly variable between individuals.

Most arrhythmias do not produce clinical signs and remain undetected throughout the horse’s life. Horses with asymptomatic arrhythmias can have successful performance careers without being affected by their condition.

Horses that are severely affected are likely to display signs associated with abnormal cardiovascular function, including: [5]

  • Shortness of breath
  • Anxiety
  • Exhaustion
  • Poor performance
  • Loss of consciousness & collapse
  • Death

If your horse is exhibiting poor performance and other signs of arrhythmia, contact your veterinarian for testing and diagnosis.

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Types of Cardiac Arrhythmias

Various types of cardiac arrhythmias can affect horses, each with distinct characteristics and implications for the equine cardiovascular system.

Some cardiac arrhythmias, such as atrial fibrillation (AF), have been thoroughly studied in performance horses and their influence on athletic ability is well understood. However, less is known about the effects of uncommon arrhythmias on horses. [6]

Sinus Tachycardia

Tachycardia in horses describes a fast heart rate of over 50 beats per minute (bpm) at re