Enlarged Heart (Dilated Cardiomyopathy) in Dogs

PetMD Editorial
By PetMD Editorial
Published: July 10, 2019
Enlarged Heart (Dilated Cardiomyopathy) in Dogs

Reviewed and updated for accuracy on July 10, 2019, by Dr. Natalie Stilwell, DVM, MS, PhD

Dilated cardiomyopathy (DCM) is a disease of the heart muscle that is characterized by an enlarged heart that does not function properly. Here’s what you need to know about cardiomyopathy in dogs, from the symptoms and how it affects their bodies to diagnosis and treatment.

What DCM Does to a Dog’s Heart and Lungs?

In most cases of DCM in dogs, the ventricles (lower chambers of the heart) become enlarged, though some cases also involve enlargement of the atria (upper heart chambers).

With DCM, the muscle wall of the heart becomes thinner, causing it to lose the ability to pump blood to the rest of the body.

As a result, fluid can accumulate in certain tissues, including the lungs.

If left untreated, the compromised heart muscle eventually becomes overwhelmed by the increased fluid volume, resulting in congestive heart failure (CHF).

Symptoms of Dilated Cardiomyopathy in Dogs

The major symptoms of DCM include:

  • Lethargy

  • Anorexia

  • Labored breathing

  • Panting

  • Coughing

  • Abdominal distension

  • Sudden collapse

In some cases, dogs with preclinical DCM (prior to the appearance of symptoms) may be given a questionable diagnosis if they appear to be in fine health.

On the other hand, a thorough physical exam can reveal some of the subtle symptoms of DCM, such as:

  • Pulse deficits

  • Premature heart contractions that originate in or above the ventricles

  • Slow capillary refill time in the mucous membrane tissues (e.g., gums are slow to turn pink again after pressing on them gently), indicating poor circulation

  • Breathing sounds muffled or crackly due to the presence of fluid in the lungs

Causes of DCM in Dogs

The incidence of DCM in dogs increases with age and usually affects dogs that are 4-10 years old.

Although the definitive cause of DCM in dogs is unknown, the disease is believed to have several factors, including nutrition, infectious disease and genetics.

Nutritional deficiencies related to taurine and carnitine have been found to contribute to the formation of DCM in certain breeds, such as Boxers and Cocker Spaniels.

Evidence also suggests that some breeds have a genetic susceptibility to DCM, such as the Doberman Pinscher, Boxer, Newfoundland, Scottish Deerhound, Irish Wolfhound, Great Dane and Cocker Spaniel. In some breeds, especially the Great Dane, males appear more susceptible to DCM than females.


In addition to a thorough physical examination, certain medical tests are needed to confirm a diagnosis of DCM in dogs and rule out other diseases.

Radiographic (X-ray) imaging may reveal that the dog has an enlarged heart as well as fluid in or surrounding the lungs.

An electrocardiogram (EKG) may reveal an arrhythmia (or irregular heartbeat) or ventricular tachycardia (abnormally rapid heartbeat). In some cases, a 24-hour EKG (Holter monitor) may be required to fully characterize abnormal heart activity.

An ultrasound of the heart, known as an echocardiogram, is required to definitively diagnose DCM. This test examines the thickness of the heart muscle and each chamber’s ability to pump blood.

In the case of DCM, an echocardiogram will reveal enlargement of one or more heart chambers, along with decreased contractile ability of the heart muscle.


Treatment for DCM is multifaceted and typically includes several medications used to increase the heart’s pumping ability and manage any arrhythmias.

A diuretic may also be administered to decrease fluid accumulation in various tissues, and a vasodilator may be given to dilate the blood vessels and improve circulation.

Except in cases where a dog is severely affected by the disease, long-term hospitalization should not be necessary.

Living and Management

Depending on the underlying cause of disease, DCM in dogs may be progressive and have no cure. Therefore, long-term prognosis is relatively poor for dogs that have clinical signs of heart failure.

Frequent follow-up examinations are typically recommended to assess progress of the disease. Assessment may include thoracic radiographs, blood pressure measurement, EKG and blood work.

You will also need to monitor your dog’s overall attitude and stay alert for any outward signs of disease progression, such as labored breathing, coughing, fainting, lethargy or a distended abdomen.

Despite therapy and conscientious care, most dogs with DCM eventually succumb to the disease.

Your veterinarian will counsel you on your pet's prognosis based on the progression of the disease at the time of diagnosis. In general, dogs with this condition are given 6-24 months to live.

Doberman Pinschers tend to be more severely affected by this disease and will generally not survive longer than six months after the diagnosis is made. In this case, your veterinarian can advise you on treatment options in order to keep your dog as comfortable as possible.

Featured Image: iStock.com/Bigandt_Photography

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