From: Equestrian and Horse | Horse Ailments
Arrhythmia
This is where the horses heart has an irregular beat that beats either too fast or too slow. The most common Arrhythmia is known as Atrial Fibrillation.
Types.
A horses normal heart beat at rest is around 36 to 42 beats per minute and with exercise this can reach 220 beats per minute.
Causes
It occurs when the electrical current to the horses heart is disturbed, blocked or disrupted, causing it to beat way too fast or far too slow. Low potassium levels can also trigger an irregular heart beat. Heart disease can also disrupt the hearts natural rhythm.
What makes the heart beat
Ions are cells within the heart that receive an electrical current that starts and controls the hearts beat. Ions are electrically charged protein cells that are made up of for example Sodium, Magnesium, Calcium and Potassium it is these that send off an electrical reaction to get the heart beating.
Symptoms
Treatment
Is to restore the horses natural rhythm, so that the heart beats in a regular fashion. The Vet will first listen to the heart rate and will often use an electrocardiogram to monitor the heart more closely. Treatment can include the use of drugs to restore the hearts natural beating rhythm or in some cases the use of surgery to help restore the hearts natural beating rhythm back to normal.