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My Dog’s Heart Is Beating Irregularly — Causes of Atrial Fibrillation and When to Seek Veterinary Care

HeartQ&AMeongsiljang Veterinary Advisory Board

Canine arrhythmia (atrial fibrillation) is a condition characterized by an irregular heartbeat, making early detection and proper management essential. Here’s a summary of the key information every pet owner should know.

What Is Canine Arrhythmia (Atrial Fibrillation)?

Diagram of a dog’s heart structure in atrial fibrillation

Canine arrhythmia (atrial fibrillation) is a heart rhythm disorder in which the heart’s atria beat irregularly. In a healthy heart, contractions occur in a regular pattern, but with this condition, disorganized electrical signals in the atria prevent coordinated contraction, causing the heart to beat rapidly and irregularly. This state impairs the heart’s ability to pump blood effectively, leading to symptoms such as lethargy, exercise intolerance, and decreased energy. In severe cases, it can progress to congestive heart failure or cause a sudden decline in cardiac function. It is relatively common in large and giant breed dogs, as well as in older dogs, making early detection and consistent management essential.

What Are the Main Causes of Arrhythmia (Atrial Fibrillation)?

The causes of atrial fibrillation in dogs are varied, including structural heart abnormalities, aging, and complications from other heart diseases. It is particularly common in large and giant breeds, and in some large dogs, it can occur even when the heart structure is normal. The risk increases significantly with underlying conditions that cause atrial enlargement, such as dilated cardiomyopathy (DCM) or heart valve (mitral valve) disease, and it is frequently observed when left atrial enlargement is present. The likelihood of occurrence increases with age, and autonomic nervous system imbalance or toxicity from medications like digoxin can also trigger rhythm abnormalities.

Monitoring image of a puppy with an irregular heart rhythm

What Are the Main Symptoms of Atrial Fibrillation?

Symptoms of arrhythmia (atrial fibrillation) in dogs can vary widely, and in the early stages, there may be no noticeable signs. However, in severe cases, symptoms such as difficulty breathing, fatigue, fainting, an increased heart rate, and easy exhaustion after exercise may appear. Dogs may suddenly stop or collapse during walks, and in severe cases, they may exhibit behaviors suggesting they are aware of their heartbeat. This indicates that the heart is not pumping blood effectively, leading to insufficient oxygen supply to the brain and other organs.

Signs That Require Immediate Veterinary Visit

If your dog suddenly collapses, experiences rapid breathing, has a bluish tint to their mouth, or shows signs of trembling due to an abnormally fast heart rate, you should seek immediate veterinary care. These symptoms may indicate a life-threatening emergency caused by heart dysfunction. In particular, if your dog recovers slowly after fainting or collapses repeatedly, urgent medical attention is essential.

Stage-by-Stage Symptoms of Atrial Fibrillation and How to Respond

Item	Main Symptoms	Response Measures
Mild	Asymptomatic or mild fatigue	Detected during regular check-ups such as ECG, observe course without medication
Moderate	Easily tired after walks, lethargy, irregular heartbeat	Take heart rate control medication, regular monitoring
Severe	Fainting, difficulty breathing, very rapid and irregular heartbeat	Visit hospital immediately, consider medication or electric shock (defibrillation) treatment

If symptoms worsen, consult your veterinarian immediately.

How Is Diagnosis Performed?

Canine arrhythmia (atrial fibrillation) is diagnosed using an electrocardiogram (ECG), which measures the heart's electrical activity. Since irregular rhythms may not be detected by routine heart rate checks, it is important to capture them through 24-hour heart monitoring (Holter monitoring). Additionally, an echocardiogram (heart ultrasound) is used to evaluate the structure and function of the heart and to check for underlying conditions. Multiple tests are performed in combination to ensure an accurate diagnosis.

A puppy wearing a 24-hour heart monitoring device

What Are the Treatment Options?

Treatment for atrial fibrillation is tailored to each individual case. - Medication: Therapy focuses on controlling heart rate or restoring normal rhythm (sinus rhythm). Digoxin is commonly used for rate control, while antiarrhythmic drugs like amiodarone may be considered when rhythm conversion is needed. Your veterinarian will determine the appropriate medication and dosage based on your pet’s condition. - Electrical Cardioversion: If medication is ineffective or if there is minimal atrial remodeling, electrical cardioversion may be used to restore normal heart rhythm. - Management of Underlying Conditions: If an underlying cause such as dilated cardiomyopathy or valvular heart disease is present, it will be treated concurrently. Congestive heart failure is managed with diuretics, ACE inhibitors, pimobendan, and other supportive medications. - Regular Monitoring: Frequent communication with your veterinarian is essential to monitor medication effectiveness and track any changes in your pet’s condition. Consistency and ongoing care are key to successful treatment.

A veterinarian preparing a cardiac medication injection

Key Points for Home Care

Consistent at-home care is crucial for managing your dog’s atrial fibrillation, directly impacting both survival and quality of life. - Medication Administration: Give medication daily at the exact prescribed time and dosage. Missing doses can cause the heart rhythm to become irregular again. - Stress Management: Maintain a quiet environment and avoid sudden noises or changes that could startle your pet. - Exercise Moderation: Excessive exercise increases cardiac strain. Focus on short walks and ample rest. - Dietary Management: Feed a low-sodium, balanced diet to prevent weight gain. - Regular Check-ups: Consult with your veterinarian every 1–3 months to monitor your dog’s condition. Effective management comes from incorporating these small habits into your daily routine.

A puppy resting in a calm and stable environment

Breeds and Ages to Watch Out For

Large and giant breed dogs are at a relatively higher risk of developing atrial fibrillation, and some large breeds can experience arrhythmias even with structurally normal hearts. Additionally, extra caution is advised for dogs with enlarged atria due to conditions like dilated cardiomyopathy or valvular disease, as well as for senior dogs with weakened heart function. For these dogs, regular cardiac screenings, including electrocardiograms and Holter monitoring, are recommended to enable early detection before symptoms appear.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can atrial fibrillation be treated?

Atrial fibrillation can be difficult to fully reverse once it occurs, but symptoms can be well managed with medication and care. In some cases, electrical cardioversion may also be considered.

Can my dog go for walks if they have atrial fibrillation?

When medication is well-controlled and there are no symptoms, light walks are possible. However, avoid excessive exercise and follow your veterinarian's instructions.

Is it safe for my pet to take heart medication long-term?

Heart medications may need to be taken long-term. Your veterinarian will regularly monitor your pet’s condition and adjust the medication as needed.

Is atrial fibrillation hereditary?

This condition is more common in large and giant breeds and is closely linked to underlying diseases that cause the atria to enlarge, such as dilated cardiomyopathy or valvular disease. If you have a large breed dog, regular heart check-ups can help catch issues early.

What should I do if my pet recovers slowly after fainting?

If recovery after fainting is slow or if episodes recur, seek veterinary care immediately. This could indicate a heart condition, so prompt evaluation is essential.