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Heart Beat Problems (Premature Complexes) in Dogs

Atrial Premature Complexes in Dogs

A dog’s heart comprises four chambers: the two atria (singular: atrium) and the two ventricles. Normally, the heart maintains a highly synchronized rhythm between its various atrial and ventricular components, ensuring a consistent pattern of beats. Atrial premature complexes (APCs) disrupt this rhythm, causing the heart to beat prematurely, ahead of its usual pace.

While congenital heart defects can affect some animals from birth, APCs typically afflict older dogs, particularly those of small breeds. Detectable on an electrocardiogram (EKG), APCs manifest as premature waves known as P waves. These P waves may exhibit various characteristics such as being biphasic, negative, positive, or overlapping with the preceding T wave on the EKG.

In an EKG reading, the P wave signifies the electrical conduction originating from the heart’s sinoatrial node and traveling through the atria. The subsequent QRS complex represents the propagation of this impulse through the ventricles following its passage through the atrioventricular node. Finally, the T wave denotes ventricular recovery before the onset of the next cardiac contraction.

An increase in the automaticity of atrial muscle fibers or the presence of a single reentrant circuit can trigger premature P waves. These ectopic beats originate outside the sinoatrial node, the heart’s primary pacemaker, and disrupt the normal sinus rhythm for one or more beats.

Symptoms and Types

While atrial premature complexes may not always exhibit symptoms, particularly in older or less active dogs, some common signs to watch for include:

  • Coughing and difficulty breathing
  • Reduced tolerance for exercise
  • Fainting episodes (syncope)
  • Presence of a cardiac murmur
  • Irregular heart rhythm


The causes of atrial premature complexes can include:

  • Chronic heart valve disease
  • Congenital heart defects present from birth
  • Heart muscle disease
  • Electrolyte imbalances
  • Neoplasia (abnormal tissue growth)
  • Hyperthyroidism
  • Toxemias resulting from toxic substances in the blood
  • Drug toxicity, such as overdosing on digitalis, a heart medication
  • Normal variations commonly observed in many older dogs


To diagnose atrial premature complexes in your dog, your veterinarian will require a detailed history of your pet’s health leading up to the onset of symptoms. A comprehensive physical examination will be conducted, which may include a chemical blood profile, a complete blood count, and an electrolyte panel.

Identifying an underlying cause for the heart condition that triggers APCs is crucial. An electrocardiogram (EKG) recording will be used to assess the electrical currents within the heart muscles, potentially revealing abnormalities in cardiac electrical conduction, which is fundamental to the heart’s ability to contract and beat. Additional diagnostic tools such as echocardiography and Doppler ultrasound may be employed to visualize the heart’s structure and performance, including rhythms and contraction velocity.


The treatment plan implemented by your veterinarian will be contingent upon the specific type and severity of heart disease affecting your pet. Various medications may be utilized based on the type of heart disease identified. In cases of congestive heart failure, a diuretic may be prescribed to alleviate fluid buildup, alongside a vasodilator to widen blood vessels. Digitoxin might also be prescribed to reduce the heart rate and enhance cardiac contractility.

Living and Management

Managing the condition involves treating and controlling underlying cardiac diseases under the guidance of your veterinarian. This necessitates regular follow-up appointments to monitor your dog’s progress. Despite medication, some animals may experience increased occurrences of APCs or worsen into more severe signs of heart disease as the underlying condition advances.

Depending on the specific cardiac ailment, dietary adjustments such as transitioning to a low-sodium diet may be necessary. Adjustments to your daily routine with your dog might also be needed, reducing physical exertion to ease the workload on the heart. Your veterinarian will provide guidance on the appropriate diet and level of activity required to maintain your dog’s optimal health.

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