You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Atrial fibrillation is a common diagnosis in veterinary medicine - particularly in some large breed dogs - but what is it ?

The heart consists of 4 chambers - two ventricles, and two atria. The atria and ventricles are hollow chambers surrounded by a muscular wall which also contains nerve tissue and blood vessels. Blood arrives back from the body into the heart via the main vein - the vena cava (which empties into the right atrium) or the pulmonary vein (which empties into the left atrium). Stimulation of the nerve supply makes the heart muscle contract, which forces the blood inside the chambers out, either into the next chamber (from an atrium into a ventricle) , or into one of the  blood vessels that leaves the heart (from the right ventricle into the pulmonary artery, from the left ventricle into the main artery in the body, the aorta).

In the normal heart the sequence of nerve stimulation and muscle contractions is very well co-ordinated but in "atrial fibrillation" and other disorders things go wrong.

Atrial fibrillation occurs when there is continuous disorganised nervous (electrical) activity across the atrium which results in inefficient uncontrolled contraction of the chambers muscular wall, and ultimately reduced output of blood from the heart. Abnormal electrical activity and contraction of the heart such as this is called an arrhythmia.

 Dogs with atrial fibrillation may have the following signs :

• Lethargy
• Poor exercise tolerance - reluctant or unable to exercise
• A rapid heart rate (180 - to over 300 beats per minute)
• Fluid accumulation in the abdomen (called ascites or "dropsy") - seen as swelling of the abdomen
• Enlargement of the liver - seen as swelling of the abdomen
• Fluid accumulation in the lungs, and enlargement of the atria - resulting in a cough
• Some individuals may show no signs of the disease at all

Atrial fibrillation is the most common heart arrhythmia seen in horses and cattle, and it is the second most common arrhythmia seen in humans and dogs. In dogs it often occurs secondary to other heart disease including :

• Chronic degenerative heart valve disease (endocardiosis) - which is common in older dogs.
• Heart muscle disease - dilated cardiomyopathy
• Congenital heart defects

Atrial fibrillation most often affects large and giant breeds of dog - especially the Irish Wolfhound. Affected dogs can survive for a long time with the disorder, however other cases may die suddenly. Various drugs can be used to control the signs associated with atrial fibrillation.

Last updated : March 2008