Common Heart Diseases in Dogs Part II: Sac and Muscle

A couple months ago, we discussed heart diseases in dogs that involved valves or holes. Indeed, 75% of all heart disease diagnoses in dogs involve a degenerative valve disorder. Dilated Cardiomyopathy (DCM) is the second most diagnosed heart disease, but makes up less than 25% of all cases.

Some of the information presented will be a review from our last post.

The Heart’s Basic Anatomy

The heart is one of the most complicated organs in the body. We are simplifying this review of the anatomy and physiology to just the basics.

The pericardium is a membrane – or sac – that surrounds the heart. The muscles of the heart, termed the myocardium, make up the middle and thickest layer of the heart wall. “Myo” refers to muscle.

The heart has four main arteries: Left Coronary, Right Coronary, Aorta and Pulmonary. Think of them as the highways of the body.

The heart has four chambers: Left Atrium, Left Ventricle, Right Atrium and Right Ventricle.

Valves are located between each of the chambers. Valves are flaps that prevent blood from flowing in the wrong direction or backwards. When the valve is faulty, this backward flow can occur. Think of a valve as a dam, a gate or a guard. The primary valves are: Mitral, Aortic, Tricuspid, and Pulmonary.

Signs That Your Dog May Have a Heart Condition

These are the signs to look for at home and to relay to your veterinarian: persistent cough, difficulty breathing, fainting or collapse, fluid accumulation around the belly, behavior changes, and inability to exercise. Yes; these signs may signal other diseases as well.

Pericardial Disease

Remember in Downton Abbey when Dr. Clarkson removed fluid from Drake’s chest at the insistence of Isobel Crawley and the protestation of the Dowager, Lady Grantham? They called it “Dropsy”. His medical condition is actually termed pericardial disease or pericardial effusion, whereby the sac of the pericardium fills with fluid. The pressure from the fluid compresses the heart.

As previously mentioned, the pericardium is the membrane surrounding the heart. When fluid builds up in the pericardium, pressure is increased on the heart. When this occurs, a companion dog may have swollen neck veins, may accumulate fluid around the belly, may collapse, may vomit, and may have an increase in breathing rate.

Thus far, we have classified the two most common root causes of pericardial disease as either inflammation due to an unknown cause (pericarditis), or benign or cancerous tumors. Yes; other conditions – congestive heart failure, infections, and trauma – can cause pericardial effusion. However, once those and tumors are ruled out, the disease is labeled as idiopathic.

Pericardial effusion requires emergency care that will require the procedure (pericardiocentesis), as Dr. Clarkson performed on Drake. Pericardiocentesis will buy time to figure out the cause and can be performed again, if needed.

In the case of persistent idiopathic inflammation, the pericardium can have a ‘window’ cut out of it or can even be removed. If benign cardiac tumors are the cause, these can be surgically removed. The prognosis with cancerous tumors (such as hemangiosarcoma) is not good. Yes; there are options, but until treatment options improve, a companion pet parent may want to consider palliative care and the humane decision for the pet.


Cardiomyopathy is any disease that primarily involves the heart muscle.

Dilated Cardiomyopathy (DCM)

DCM is the heart’s loss of muscle function or strength involving the left ventricle. The muscle stretches and thins and makes it difficult to pump blood to the rest of the body. It is the second most commonly diagnosed heart disease in dogs after Degenerative Valve Disease, which accounts for approximately 75% of all diagnoses of heart disease.

Signs include weakness, collapse, fainting, difficulty breathing, coughing, and accumulation of fluid in the chest or abdomen. Veterinarians will detect a heart murmur and possible arrhythmia.

DCM is a significant concern. We know that certain things like Doxorubicin (a chemotherapy drug) and parvovirus infections can cause or lead to DCM. Once we rule those out as possible causes, what are we left with?

While we know about the genetic mutation in Doberman Pinschers, we have not yet definitively identified the genetic component for other breeds or if the disease is genetic plus something else such as diet or lifestyle. For instance, American Cocker Spaniels are predisposed to the disease, but many respond to taurine supplementation, an amino acid. Other dogs respond to another amino acid, carnitine.

Most often, we see DCM in large breeds like the Great Dane, German Shepherd, Irish Wolfhound, Scottish Deerhound, Newfoundland, Saint Bernard, and Labrador Retriever that are middle-aged or geriatric.

Much of the DCM research these days revolves around nutrition. This is a good place to start. Some scientists may still believe that grain-free foods are the main cause, but the Food and Drug Administration (FDA) has determined there is no cause-and-effect relationship between grain-free foods and the rising cases of DCM. We, at Hemopet, agree that there is no link at this point in time.

So, we predominantly have the influences of genes, nutrition, amino acids, older, and large dogs. Dogs are living longer than before. Diagnostic testing is more precise and available than before. Even though genetic testing for people and animals has escalated in leaps and bounds in a short period of time, more needs to be completed. Finally, nutritional guidelines for dogs are primarily based on feeding trials from over 30 years ago with small to medium-sized dogs or puppies. Clearly, more research is needed.

If a companion dog is diagnosed with DCM, veterinarians typically prescribe pimobendan and an ACE-inhibitor such as benazepril or enalapril. Other medications are available as well.

Hypertrophic cardiomyopathy (HCM) is a rare disorder in dogs.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

ARVC primarily affects Boxers and is often referred to as “Boxer Cardiomyopathy.” Whereas DCM affects the left ventricle, On the other hand, ARVC affects the right one. Sometimes, the condition progresses to the extent that eventually DCM sets in. If ARVC is suspected due to a fast heart rate (tachycardia) or fainting, dogs should be outfitted with a Holter monitor for 24 hours. They can also be prescribed medications to regulate their heart rates.

Persistent Atrial Standstill (PAS)

PAS is another type of cardiomyopathy. This is distinct from DCM in that the heart muscle that lies in the middle part of the heart deteriorates. However, PAS presents like DCM.

In late stages, mitral regurgitation may occur (backward flow of blood through the mitral valve). We see PAS in the English Springer Spaniel, Old English Sheepdog, Shih Tzu, German Shorthaired Pointer, and mixed-breed dogs. While a pacemaker can be implanted, the prognosis is often poor.

This makes us wonder if some dogs, suspected to have DCM during the controversy, actually had PAS and did not have an echocardiogram performed for confirmation. We just will never know.

Pericardial/Cardiomyopathy References

“Circulatory System.” Merck Veterinary Manual, 2023,

Mansilla, Wilfredo D et al. “Minimum dietary methionine requirements in Miniature Dachshund, Beagle, and Labrador Retriever adult dogs using the indicator amino acid oxidation technique.” Journal of animal science vol. 98,11 (2020): skaa324. doi:10.1093/jas/skaa324,

Thomason, Justin D et al. “Survival of 4 dogs with persistent atrial standstill treated by pacemaker implantation.” The Canadian veterinary journal = La revue veterinaire canadienne vol. 57,3 (2016): 297-8,

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