Dog Heart Diseases – Symptoms and Treatments

Approximately 10% of canines examined by veterinarians suffer from some of the common dog heart diseases. They are also referred to as cardiovascular illnesses. Unlike the ones affecting other organs and body systems, cardiovascular problems rarely go away on their own.

What are dog heart diseases? Dog heart disease is a catch-all term for any abnormality of the heart. There is a wide range of health conditions that can be described as heart diseases. Some encompass problems with the physical structure or the electrical activity of the function of the heart.

Various methods can be used to classify heart diseases in dogs. For example, if the dog had the problem at birth it’s classified as a congenital heart issue, if not, it’s acquired.

According to the various causes for dog heart diseases they can be degenerative or infectious for example. The clinical status of the dog is described as a left-heart failure, right heart failure, biventricular, etc.

Are dog heart diseases serious? Yes, dog heart diseases can be very serious and lead to death. Some of them are well hidden and the owners may be unaware of them even existing. That’s why regular veterinary check-ups are important to detect such problems early on.

Any heart abnormality that becomes so severe that it prevents the heart from pumping enough blood and satisfying the needs of the body is called heart failure or heart congestion.

It’s important to remember that there are many cases when a heart disease won’t ever become so severe to cause heart failure.

Common abnormalities that can lead to cardiovascular or heart diseases in dogs include:

·         Mitral Valve Disease

·         Dilated Cardiomyopathy

·         Arrhythmic Cardiomyopathy

·         Heartworm Disease

Mitral Valve Disease

The heart is an organ that has 4 chambers. There are two upper ones called atria (left and right) and two lower chambers known as ventricles (left and right).

Between the corresponding chambers, there is a valve that keeps the blood from the backward flow. The valve between the left upper chamber and the left lower chamber is called the mitral valve.

Credit PetMed

The disease starts when the valve wears out over time and lets blood come back to the upper chamber. The reason for the functional insufficiency can be rupture of the fibrous cords holding it in place and infections of the valve.

Mitral valve disease in dogs is a very common condition. Approximately 1 in 10 dogs will develop this illness throughout their lifetime. Of all cases of heart diseases in dogs, MVD accounts for about 80% of them.

It’s more common in small breeds of dogs.  

What happens in the case of MVD?

The excess blood in the left side of the heart slowly goes back to the lungs. Because the lungs are now overflowed, a small amount of liquid leaks out into the airways. In much-progressed cases, fluid also builds up in the abdomen and other body tissues.

Symptoms, diagnosis, and treatment of MVD

The first sign of MVD in dogs is a heart murmur. The murmur is the sound of the blood going back into the left atrium with turbulent flow. It usually happens in dogs 4 to 6 years of age.

Around this period there are no obvious symptoms of the disease. The more blood flows back the more the heart’s efficiency is reduced with congestive failure (heart failure) as a result. It can take from months to years for this to happen.

Symptoms of the disease include:

·         Gagging (like the dog is trying to clean its throat)

·         Chronic cough

·         Lack of stamina

Early diagnosis is important because the severity of the symptoms only depends on the progression of the disease.

Mitral Valve Disease in dogs is diagnosed with several tests that provide information for different aspects of the dog’s heart function. The process starts with a physical examination followed by listening to the heart and the lungs, x-rays, blood and urine tests ECG, and ultrasound.

A dysfunctional or leaky mitral valve in people is surgically replaced; however such procedures are not frequently performed in dogs. Treatment can provide alleviation of symptoms though.

The most commonly used drugs are ACE inhibitors. They work by lowering the blood pressure and enalapril and benazepril are the first choices of treatment. Diuretics such as furosemide can help by stimulating the kidneys to remove excess fluid. 

A whole other spectrum of vasodilators, cardiac glycosides, inotropes, and beta-blockers can be used following the dog’s current health status. A low-sodium diet is preferred because too much salt prevents the elimination of fluids from the body.

For most pups, the treatment is a long-term commitment. It’s not too expensive to get all the medications and the veterinary diet, but it’s not too cheap as well.

Dilated Cardiomyopathy in Dogs

Dilated Cardiomyopathy in dogs is a serious condition. The heart muscle degenerates and becomes thinner over time. The muscle wall of the left ventricle is particularly affected.

Too much blood collects in the heart chambers causing the walls to stretch in what soon appears as a much larger than normal heart – that’s how the disease got the name.

Credit PDSA

This disease is a lot more frequent in large breeds of dogs. The most commonly affected breeds are Boxers, Dobermans, German Shepherds, Saint Bernards, Irish Wolfhounds etc.

Cases in small dogs are very rare. An interesting fact is that males get DCM a lot more than female dogs.

Symptoms, diagnosis, and treatment of DCM

Once it begins this illness develops subtly and slowly. The first symptoms may appear suddenly in the form of:

·         Rapid breathing (when resting/sleeping)

·         Increased effort when breathing

·         Restlessness when sleeping

·         Gagging/coughing

·         Weakness

·         Exercise intolerance

·         Collapse

·         Reduced appetite

·         Weight loss

·         Distended abdomen

·         Depression and lack of interaction

·         Sudden death

It happens often enough for the dog to develop congestive heart failure when he hasn’t been diagnosed and treated for Dilated Cardiomyopathy on time. In just a few hours congestive heart failure can manifest with blue tongue, excessive drooling, heavy breathing, collapse, and death. 

In case the vet suspects this disease he/she will need to listen to the chest with a stethoscope and determine the presence, location, and intensity of heart murmurs. The strength and the rhythm of the heart are also assessed.

Besides the usual blood and urine tests, x-ray images are needed to visualize the size of the heart. With ultrasound, the thickness of the walls can be accurately determined. Treatment can only start after a few of the tests have been performed.

Dogs primarily start taking diuretics and ACE inhibitors to control blood pressure and remove excess fluids from the body. Other heart medications can help when there is associated arrhythmia.

Arrhythmic Cardiomyopathy

Arrhythmic Cardiomyopathy is an inherited disease that primarily affects Boxers. Although other dog breeds can also get it, it’s very rare. It’s most likely to develop when the dogs are 5-7 years of age.

A deletion in an important heart gene has been identified as the main cause of the disease. Approximately 40% of Boxers have this genetic mutation. There are DNA tests available to determine if a dog has it.

With AC the heart muscle is replaced with fatty and fibrous tissue. Without enough muscle, there is electrical instability and the heart rhythm can’t maintain its regularity.

Symptoms Diagnosis and Treatment of Arrhythmic Cardiomyopathy 

AC produces heart arrhythmias (irregular heartbeat) that sometimes can be detected on physical examination.

The most common symptom of the condition is collapse or fainting episodes – they are called syncope. It’s not uncommon for dogs to die suddenly without any previous signs.

While syncope is the only symptom in most cases, some additional signs can be:

·         Coughing

·         Shortness of breath

·         Exercise intolerance

·         Restlessness while resting

Dogs suspected of AC should be thoroughly checked by a veterinarian and go through an ECG, ultrasound, and blood pressure examination.

To evaluate the severity of the arrhythmia it’s best to perform a Holter monitor on the dog. A Holter monitor is an ECG worn at home that allows the cardiologist to see the heart rhythm during usual daily activities.  

The treatment plan depends on the severity of the condition. Every dog needs to take antiarrhythmic drugs that help control the heartbeat. During the treatment, the patients can also use a Holter monitor to evaluate the efficiency of the drugs.

Many dogs manage to live a normal lifespan with appropriate medications and regular veterinary check-ups.

Heartworm disease

Heartworm disease in dogs is caused by a parasite called Dirofilaria immitis. Adult worms can be found in large quantities in the heart and the large blood vessels including the pulmonary artery.

Credit North Ogden Animal Hospital

Sometimes worms can migrate to other marginal places of the circulatory system in dogs. At the time of diagnosis one dog can have as many as 300 adult worms in him.

Adult heartworms live 5 years. The females produce millions of microfilaria during that time. It’s a very serious disease for canines that can be found everywhere in the world.

Heartworm cycle

Dogs get infected with heartworm when a mosquito carrying the parasites bites them. Nearly 30 different species of mosquitoes can transmit this disease. When they attach to a dog’s capillaries they release infective larvae.

The larvae travel through the bloodstream to the heart and the surrounding blood vessels. Once they settle they continue maturing and start mating within half a year.

Heartworm symptoms

Once the parasites enter the dog’s body it can take years before there are any evident signs of infestation. In the majority of dogs, heartworm disease is diagnosed when they are 2 years old or less. It’s very rare to find it in puppies less than 12 months of age.

The main problem is that by the time the symptoms are apparent the disease is already in advanced form. Adult heartworms clog both the heart and the main blood vessels. Sometimes they even destroy the heart valves.

The more severe the symptoms are the larger the numbers of adult heartworms in the dog’s bloodstream are. What we usually see in dogs is:

·         Dry cough

·         Shortness of breath

·         Weakness

·         Loss of stamina

·         Pale gums

·         Listlessness

All of the symptoms become more pronounced after the dog has been exercising or simply walking for some time.

Many dogs start losing weight and end up in poor body condition.

Diagnosis and treatment of heartworm

The veterinarian will ask for a full medical history and listen to the abnormal heart and lung sounds. Also, he/she would probably like to know whether the dog has been treated with insect repellents regularly.

Few simple blood tests are often enough to make a final diagnosis. If they offer additional tests at the vet clinic it’s probably because they want to acknowledge whether the dog can safely undergo the heartworm treatment.

An injectable new drug called Melarsomine is used to eliminate adult heartworms in the dog’s bloodstream. Usually, dogs receive one shot followed by a month of rest and two more shots in a 24 hours interval.

Ivermectin, an anti-parasitic drug was widely used for the treatment of heartworm in dogs though it’s less and less attractive because of the negative effects.

Sometimes the antibiotic doxycycline is used as a concurrent therapy. While doxycycline doesn’t kill the parasite it combats a bacteria called Wolbachia that lives in the parasite’s digestive tract.

All dogs must rest a lot while they are treated for heartworm disease. The dead adult worms start to decompose in the small blood vessels of the lungs. That’s why a cough that lasts for almost 2 months can be noted in dogs that underwent treatment.

When the dog gets better you need to stay vigilant about external parasite prevention because there is no guarantee that your dog can’t get infested with heartworms once more.


The thing about all dog heart diseases is that they get clinically significant when they are in a progressed state. Maintaining a regular check-up schedule can be a life-saving habit for your dog.

All veterinarians will be more than glad to see their patients more often and maintain their good health rather than fix things that are already beyond repair.  

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About The Rotty lover 2159 Articles
My name is Dr. Winnie. I earned a Bachelor of Science in Psychology from Duke University, a Masters of Science in Biology from St Georges University, and graduated from the University of Pretoria Veterinary School in South Africa. I have been an animal lover and owners all my life having owned a Rottweiler named Duke, a Pekingese named Athena and now a Bull Mastiff named George, also known as big G! I'm also an amateur equestrian and love working with horses. I'm a full-time Veterinarian in South Africa specializing in internal medicine for large breed dogs. I enjoy spending time with my husband, 2 kids and Big G in my free time. Author and Contribturor at SeniorTailWaggers, A Love of Rottweilers, DogsCatsPets and TheDogsBone