Irregular Heart Beat in Dogs

By PetMD Editorial on Feb. 25, 2010

Ventricular Premature Complexes in Dogs

In order to pump blood to the lungs and body, the heart must work in a coordinated fashion. The heart has an electrical conduction system that is responsible for controlling the heart rate. This electrical conduction system generates electrical impulses (waves), which propagate throughout the musculature of the heart, stimulating the heart's muscles to contract and push blood through the interior arteries and out into the body. There are two nodes (masses of tissue) present in the heart that play an important role in this conduction system. The sinus node, or sinoatrial (SA) node, is a clustered collection of similar cells located in the right atrium, its purpose being to generate electrical impulses and to serve as the heart's pacemaker. The other node is called the atrioventricular (AV) node. Like the SA node, it is a clustered collection of similar cells situated in the right atrium, close to the ventricle. The AV node receives impulses from the SA node, and after a small delay, directs the impulses to the ventricles. This delay allows for the atrium to eject blood into the ventricle before the ventricular muscles contract. The AV node can also take the place of the SA node as the heart's pacemaker, should the SA node be affected adversely by a pathological condition of the heart.

Ventricular premature complexes are a type of irregular heart beat. An electrical impulse is initiated within the ventricles instead of the SA node, causing the ventricles to contract too early (thus the “premature” in ventricular premature complexes).

Ventricular premature complexes on a recording of an electrocardiogram (ECG) are characterized by abnormal (too wide and/or oddly shaped) QRS complexes, the state that indicates the change in electrical potential in a single heartbeat. They are not associated with P waves.

Symptoms and Types

  • Weakness
  • Exercise intolerance
  • Fainting
  • Often asymptomatic
  • Cough if caused by congestive heart failure (CHF)
  • Difficulty breathing if caused by CHF
  • Sudden death


  • Cardiomyopathy
  • Congenital defects (especially subaortic stenosis)
  • Chronic valve disease (heart disease)
  • Gastric dilation and volvulus (stomach turns and flips on itself)
  • Traumatic inflammation of the heart
  • Digitalis toxicity (heart medication)
  • Cancer of the heart
  • Myocarditis
  • Pancreatitis

Other factors that may predispose a dog to ventricular premature complexes are:

  • Low blood magnesium
  • Acid-base disturbances
  • Low blood oxygen


Your veterinarian will perform a thorough physical exam on your dog, taking into account the background history of symptoms and possible incidents that might have led to this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. The electrolyte panel will show if there is hypokalemia and hypomagnesemia. If present, bloodwork will also confirm pancreatitis.

An echocardiogram of the heart should be performed to check for structural heart disease. Long-term ambulatory (Holter) recording of the ECG can be done to detect transient ventricular arrhythmias in patients with unexplained fainting or weakness.


Most patients can be treated on an outpatient basis. However, patients with an electrolyte imbalance (hypokalemia or hypomagnesemia) should be hospitalized temporarily for  fluid therapy with electrolytes to correct the imbalance. Oxygen therapy will need to be given if your dog is hypoxemic. Your veterinarian may prescribe anti-arrhythmic drugs to your dog, depending on the underlying cause of the ventricular premature complexes.

Living and Management

The prognosis is uncertain and depends on whether the underlying cause can be treated. Be aware that the arrhythmia may worsen and/or fainting or sudden death can occur. If the heart has a structural disease (which your veterinarian will inform you of, if this is the case) or if your dog is showing clinical signs of the arrhythmia, you will need to restrict your dog's activity. Your doctor will advise you on an appropriate physical routine, and will schedule follow-up appointments with you for your dog as is necessary to treat the underlying disease. 

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