Dilated Cardiomyopathy (DCM) in Dogs: Signs, Causes, and Treatments

Dilated cardiomyopathy (DCM) is a serious heart condition that can significantly affect your dog’s quality of life. Our MedVet cardiology team shares what you need to know about the signs, causes, treatment options, and prognosis for dogs with dilated cardiomyopathy (DCM). 

What is Dilated Cardiomyopathy (DCM) in Dogs?

Dilated cardiomyopathy is a condition that causes the heart muscle to become weak and thin, reducing its ability to pump blood effectively. This condition can affect one or both sides of the heart; however, the left side is more commonly involved. As the disease worsens, the heart becomes less effective at circulating oxygen-rich blood throughout the body to vital organs, such as the kidneys, brain, and liver. Over time, blood may begin to back up within the heart, causing it to stretch and contributing to its enlarged, or dilated, appearance. In some cases, the heart walls and valves stretch, allowing blood to leak across one or more valves. This leakage can create a heart murmur, which your veterinarian can hear with a stethoscope.  

Signs of an Enlarged Heart in Dogs

Dogs with DCM may develop clinical signs when the heart can no longer circulate oxygen-rich blood effectively throughout the body. In severe cases, congestive heart failure can develop, leading to fluid buildup in the lungs or abdomen. Some dogs may also develop abnormal heart rhythms (arrhythmias), which can increase the risk of fainting or sudden death.  

The signs of DCM can vary depending on disease severity, but common signs include:  

• Fatigue or weakness  

• Difficulty breathing or rapid breathing   

• Coughing, especially at night or after exercise   

• Reduced appetite or weight loss  

• Fainting or collapse, also called syncope  

• Abdominal swelling or distension  

• Pale or bluish gums or tongue 

These signs can also occur with other medical conditions, so it is important to contact your family veterinarian if you notice any of them. An accurate diagnosis can help determine the most appropriate treatment plan for your dog.  

Causes of Dilated Cardiomyopathy in Dogs

Dilated cardiomyopathy can occur in dogs of any breed, but it is most diagnosed in dogs between four and 10 years old. The exact cause is often unknown, but several factors may contribute to DCM, including:  

• Genetics: The most common form of DCM is inherited and is seen more frequently in large and giant breed dogs, including Boxers, Dalmatians, Doberman Pinschers, Great Danes, Irish Wolfhounds, Newfoundlands, and Saint Bernards. This form is often referred to as primary or idiopathic DCM. Genetic testing for mutations associated with DCM can be performed in some breeds. Other breeds, such as Cocker Spaniels, English Springer Spaniels, Portuguese Water Dogs, and Welsh Corgis, may also carry an inherited predisposition.   

• Myocarditis: Myocarditis is inflammation of the heart muscle, often caused by infection or immune-mediated disease.   

• Tachycardia: Tachycardia refers to an abnormally fast heart rate. In some cases, persistent fast heart rhythms can weaken the heart muscle over time and contribute to DCM.   

• Nutritional deficiencies: Deficiencies in nutrients such as taurine or carnitine have been associated with DCM in some dogs. Certain diets, particularly boutique, exotic-ingredient and grain-free (BEG) diets, have been investigated for a possible association with diet-related dilated cardiomyopathy. Many of the diets studied were labeled as grain-free and contained items such as dried seeds of chickpeas, beans, lentils, peas, and/or potatoes among the first five ingredients. The relationship between diet and DCM in dogs is complex, is not yet fully understood, and continues to be studied.  

• Other medical conditions and medications: Conditions such as thyroid disease, some infectious diseases, and certain medications, including doxorubicin, a chemotherapy drug, may also increase the risk of developing DCM.  

How is Dilated Cardiomyopathy in Dogs Diagnosed?

Dilated cardiomyopathy is diagnosed with an echocardiogram, or ultrasound of the heart. This test allows a veterinarian or veterinary cardiologist to evaluate the heart’s size, structure, and pumping ability in real time.  

In some cases, your veterinarian may suspect dilated cardiomyopathy (DCM) based on your dog’s breed, clinical signs, and physical exam findings. To confirm the diagnosis and better understand your dog’s heart health, additional testing is often recommended. 

Additional tests may help assess the severity of the disease and guide a personalized treatment plan. A chest X-ray can help identify heart enlargement or fluid buildup in the lungs. An electrocardiogram (ECG or EKG) evaluates the heart’s electrical activity and can detect abnormal heart rhythms. A Holter monitor, or portable heart rhythm device, may be recommended in certain breeds, or when an abnormal heartbeat (arrythmia) is detected.  

Treatment Options for Enlarged Heart in Dogs

While there is no cure for idiopathic (unknown cause) dilated cardiomyopathy, treatment focuses on managing symptoms, slowing disease progression, and improving quality of life. 

Treatment recommendations vary depending on the severity of the disease and your dog’s individual needs. Medications may include pimobendan, ACE inhibitors, diuretics, anti-arrhythmic drugs, and other heart-supportive therapies to improve heart function, reduce fluid buildup, control abnormal heart rhythms, and decrease stress on the heart. In right-sided heart failure, some patients may have fluid physically removed from the abdomen and/or chest.  

Your veterinarian may also recommend lifestyle modifications, such as maintaining a healthy weight, limiting strenuous activity, and scheduling regular monitoring appointments to track disease progression. 

In some cases, dogs with diet-associated or taurine-deficient DCM may show improvement with dietary changes and supplementation. Similarly, dogs with tachycardia-induced cardiomyopathy may experience meaningful improvement once the underlying abnormal heart rhythm is brought under control. 

What to Expect from Treatment

A dog’s response to treatment can vary depending on the stage of disease, underlying cause, and overall health. 

Early diagnosis and treatment may help improve heart function, reduce clinical signs, and slow disease progression. However, dilated cardiomyopathy is typically a progressive condition, and long-term management is often necessary. 

The primary goals of treatment are to improve comfort, maintain quality of life, and help dogs live as long and as well as possible. 

Prognosis for Dogs with Dilated Cardiomyopathy

The prognosis for dogs with dilated cardiomyopathy varies widely and depends on factors such as breed, disease severity, the presence of arrhythmias, and response to treatment. 

Some dogs respond well to medication, dietary changes, and ongoing monitoring, maintaining a good quality of life for months to years. Others may experience a more rapid progression of disease. 

Staying in close communication with your veterinarian or veterinary cardiologist is essential for monitoring your dog’s condition and adjusting treatment as needed. If your dog is showing signs of heart disease, contact your family veterinarian family and they can evaluate your dog and, if appropriate, refer you to a veterinary cardiologist for advanced diagnostics and specialized care. 

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