Atrial Fibrillation in Dogs: Causes, Symptoms & Treatment

Atrial fibrillation (AF) is a frequently encountered heart irregularity in dogs that results in rapid or erratic heartbeats, known medically as an arrhythmia. This guide explains atrial fibrillation, its root causes, signs, diagnostic procedures, and the latest treatment strategies available in the U.S. in 2025, equipping you with the knowledge to help manage dogs living with this condition.

Understanding Atrial Fibrillation in Dogs

Atrial fibrillation arises when the heart’s upper chambers, the atria, fail to contract regularly and instead quiver wildly. Although the lower chambers (ventricles) still pump blood, their rhythm becomes often chaotic and fast. This irregular heartbeat reduces cardiac efficiency, potentially diminishing your dog's overall wellbeing.

What Causes Atrial Fibrillation?

Two main forms of AF occur in dogs:

• Primary Atrial Fibrillation: Rare and typically found in large or giant breeds like Irish Wolfhound puppies. This form is mainly due to enlarged heart chambers that disrupt electrical signals despite normal heart muscle function.
• Secondary Atrial Fibrillation: More prevalent, this type develops from underlying heart diseases, such as dilated cardiomyopathy—often diagnosed in breeds like Doberman Pinschers—and congestive heart failure. This form usually causes a very rapid and inefficient heartbeat and tends to have a more serious outlook.

Identifying Symptoms

Dogs with atrial fibrillation may exhibit various symptoms depending on the AF type, including:

• Exercise intolerance where they tire easily and breathe heavily compared to healthy peers.
• Rapid or labored breathing, frequently the first clinical sign observed by pet owners.
• Persistent coughing or fainting spells caused by insufficient oxygen delivery.
• Gums that appear blue, signaling inadequate oxygen in the bloodstream.
• In severe cases, particularly with secondary AF linked to cardiomyopathy, sudden collapse or unexpected death may occur.

How Is Atrial Fibrillation Diagnosed?

A vigilant veterinarian can detect the hallmark irregular heart rhythm with a stethoscope. Confirming AF and determining its cause and severity requires further testing:

• Electrocardiogram (ECG): The definitive test that registers the heart’s electrical activity.
• 24-hour Holter Monitoring: This prolonged ECG captures heart rhythms during daily activities, offering precise heart rate control assessment.
• Echocardiogram (Heart Ultrasound): Examines heart structure and reveals any underlying cardiac diseases.

Treatment and Care Management

Contemporary veterinary practice across the U.S. in 2025 centers on controlling the heart rate to enhance comfort and survival for affected dogs:

• Primary AF: Early cases (within about four months of diagnosis) may be referred to veterinary cardiologists who can attempt cardioversion, a procedure to reset the heart to a normal rhythm.
• Secondary AF: Treatment primarily involves medications like diltiazem (a calcium channel blocker) combined with digoxin (a cardiac glycoside) to slow ventricular rates and improve heart pumping efficiency. Beta-blockers are occasionally used with caution, especially in congestive heart failure cases.
• For dogs unresponsive to medication, advanced interventions such as AV node radioablation and pacemaker insertion may be conducted at specialized veterinary centers.

Ongoing monitoring, notably via 24-hour Holter ECG, allows veterinary teams to fine-tune treatments aiming to keep heart rates under 140 beats per minute, ideally below 125 bpm for best outcomes.

Importance of Prompt Veterinary Care

Timely assessment by a licensed veterinarian is crucial for managing atrial fibrillation effectively. Early detection can slow disease progression, improve life quality and duration, and prevent serious complications. If you notice symptoms like unusual breathlessness, coughing, fainting, or decreased exercise tolerance in your dog, seek veterinary consultation without delay.

Summary

Atrial fibrillation is a significant cardiac disorder usually secondary to other heart conditions. Advances in U.S. veterinary cardiology using ECG and Holter monitoring support diagnosis, while treatment focuses on controlling the heart rate to enhance survival and comfort. Responsible pet owners should pursue early veterinary diagnosis if symptoms arise and work closely with their veterinarian to optimize long-term care. This comprehensive approach maximizes wellbeing for dogs affected by atrial fibrillation.