to Pet Health Network or

Answers from vets about your dog:

Atrial Fibrillation: Why is My Dog’s Heart Beating so Fast?

Posted March 02, 2015 in Dog Diseases & Conditions A-Z

Senior dog laying down

Atrial fibrillation is an abnormal rhythm that affects the two upper chambers (atria) of the heart. During episodes of abnormal atrial rhythm, the upper chambers beat out of synch with the lower chamber (ventricles).

Cause of atrial fibrillation in dogs
Atrial fibrillation is caused by an electrical stimulus to the atrium. Atrial fibrillation may be associated with underlying heart muscle disease or it may occur in an otherwise seemingly normal heart1. It has been associated with increased size of the atrium, as occurs normally in giant breeds and as a result of atrial/ventricular valve disease.

How likely is atrial fibrillation in my dog?
The condition is more common in large breeds of dogs; for example Great Danes, Doberman Pinschers, Boxers and Irish Wolf Hounds1; but it can occur in small dogs as well2.

Clinical signs of atrial fibrillation
Atrial Fibrillation generally causes the heart to beat too fast. As a result the ventricles do not have time to normally fill and empty—ultimately resulting in heart failure.
Affected dogs may be:

  • Listless
  • Weak
  • Unable to exercise

Frequently, there is an accumulation of fluid in the lungs or abdomen. There may be an associated shortness of breath, cough or fainting3. The heart rate may exceed 200 beats per minute.

How is atrial fibrillation diagnosed and confirmed?
The physical findings associated with poor heart function and the classical abnormal rate and rhythm of the heart are the main findings to prompt a diagnosis. An EKG will show rapid irregular heartbeats. Radiographs will often show the enlargement of the heart, abnormal distension of blood vessels and fluid retention in and around the lungs.

Share This Article

Mike has more than 35 years of experience in companion animal veterinary practice and is a valued member of IDEXX’s Pet Health Network team since 2013.