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Heart Disease in Dogs: The Ultimate Guide From a Veterinarian

Old Golden Retriever walking down a forest pathway

When your dog is coughing, it can be for different reasons like allergies or a respiratory infection. However, if your veterinarian detects a heart murmur or arrhythmia during a physical exam, then your dog might have heart disease.

Types of Heart Disease in Dogs

white scruffy dog sitting in front of a wood background

Valvular diseases

Valvular diseases are disorders of the heart valves located between the chambers of the heart and blood vessels. There are four heart valves: the tricuspid valve, the pulmonic valve, the mitral valve, and the aortic valve. 

Some valvular disorders can be inherited like pulmonic stenosis and aortic stenosis, which refers to a thickening of the heart valves, making the heart work harder. Other valvular disorders can be acquired, especially in older pets and certain breeds. 

The Cavalier King Charles Spaniel dog has a higher risk of developing mitral valve insufficiency. This can be due to mitral valve dysplasia – where the valve does not develop normally as a puppy – or mitral valve regurgitation, which is when the mitral valve begins to leak over time due to higher pressure on the left side of the heart. Valves can also become infected due to bacteria in the blood supply. This is called endocarditis.

Treatment varies based on the type of valve affected and the patient’s clinical signs. Young dogs with pulmonic stenosis might be good candidates for a surgery called balloon valvuloplasty, where a balloon-like tool is surgically placed into the valve, inflated, and thus opens the constricted valve. 

Dogs with diseased mitral valves are more difficult to treat surgically. Their prognosis is typically good because the pulmonic valve is affected by pressures on the right side of the heart, which is a lower pressure area compared to the left side. The left side of the heart needs to be a higher-pressure area in order to pump blood to the entire body, and this means that the left-sided valves – mitral and aortic – can be more difficult to fix. Veterinary cardiologists can perform mitral valve replacement surgery, but this is not yet a common practice.

Heartworm disease

Small terrier running through a field of taller grass

Heartworm disease is caused by a bite from a mosquito carrying heartworm larvae called microfilaria. These microfilariae go through several stages of development in the dog’s muscle tissues and then move into the bloodstream. Once they get to the heart, they develop into full-fledged worms. A dog can have as many as three hundred heartworms once diagnosed. The worms can obstruct the chambers of the heart and the main pulmonary artery, leading to heart failure.

Treatment can be painful, expensive, and time-consuming. Your veterinarian will prescribe an oral antibiotic for four weeks called doxycycline. If your dog is coughing and showing other clinical signs, then an oral steroid will be recommended as well. Three injections are given over the span of a month, and it is extremely important to keep your dog confined for several months. This means no running off-leash and no playing, which can be difficult for high-energy dogs. Adverse reactions to treatment are possible, and sudden death is a major risk factor when pets have heartworm disease. Prevention is key! Make sure that your dog is taking heartworm prevention from your veterinarian year-round.

Myocardial disease

One of the most important myocardial diseases is dilated cardiomyopathy or DCM. The walls of the heart become dilated and thin, affecting the heart’s ability to effectively contract. This is sometimes a genetic illness but can also develop in middle-aged to older dogs. Large breed dogs like Doberman Pinschers tend to be more likely to develop DCM. Recent evidence from the FDA suggests that there may be a link between grain-free diets and the development of DCM.

Causes of Heart Disease

Golden Cocker Spaniel panting at the park on a sunny day

Some causes of heart disease have been mentioned above, such as genetic factors and breed type. Overweight pets seldom develop the kind of heart disease that overweight humans might develop, such as coronary artery disease. However, being overweight does put a bigger strain on the heart’s ability to do its job. Extra weight also makes it harder to breathe, putting even more strain on the heart. Older pets are more likely to develop a valvular disease, especially small breed dogs like Chihuahuas and Pomeranians.

Signs your dog may have heart disease

One of the biggest signs of heart disease in dogs is coughing. When the heart must work harder to pump, fluid can back up in and around the lungs, causing coughing and difficulty breathing. Fluid can also build up in other places like the hind limbs. This is called edema. In certain conditions where the heart becomes enlarged, it can apply pressure to the mainstem bronchi and the trachea – or wind-pipe – which also causes coughing. Signs can also be very subtle, such as lethargy, depression, and exercise intolerance. Appetite can also be affected, causing weight loss, and further weight loss can be related to cardiac cachexia, which is a kind of muscle wasting due to heart disease. As heart disease progresses, it can cause fainting or collapsing – aka syncope – and in some cases, sudden death.

What to do for your dog

weimaraner running on a wooded pathway looking excited

One of the most important methods for the prevention of heart disease is having your dog checked by your veterinarian at least twice a year. Heart murmurs, arrhythmias, and heartworm disease all have better outcomes when detected early. Vets can provide you with topical, oral, or injectable heartworm prevention for your dog. They can also recommend testing to help determine why your dog is coughing or has a murmur/arrhythmia.

Tests are useful to determine what kind of heart disease your dog has. Radiographs or x-rays are used to evaluate the heart’s shape and size. They can also detect abnormalities with the lungs, trachea, and the blood vessels around the heart. An echocardiogram is an ultrasound for the heart and provides more of a three-dimensional picture. It is more sensitive for detecting the thickness of the heart wall and evaluating the heart valves. An electrocardiogram or ECG is used to look for conduction disturbances or problems with the way that the nerve signal to contract the heart moves through the heart tissue. Blood pressure checks are also recommended because pets can have elevated blood pressure – or hypertension – just like in humans.

Treatment is recommended based on the condition present. Dogs with clinical signs due to valve problems or congestive heart disease may need to be on a combination of blood pressure medications, diuretics, heart contractility meds, and cough tablets. Dogs with arrhythmias can do well with anti-arrhythmic medications, and in severe cases, some need surgical implantation of a pacemaker. Orthopedic dog beds can help ease comfort in dogs who are dealing with surgical recovery and many other pains and aches associated with illness and age. 

Sold out

Lastly, diet and exercise can make a difference regardless of whether the patient is healthy or has heart disease. Keeping an ideal body condition score can add one to two years to your dog’s life expectancy, and exercise can help keep them slim and trim. There are no diets available that will prevent heart disease, and sodium intake doesn’t necessarily affect the heart the way it does in humans. Grain-free diets, however, may need to be avoided until we have more information on diet-related DCM. And if you’re planning on breeding a dog whose familial history if affected by congenital heart disease, then make sure your dog is tested for these illnesses prior to breeding.

Heart disease can be a concerning diagnosis, and in some cases, there is no ultimate fix. However, with the right testing, information, and treatment, most cases can be managed so that dogs can have minimized clinical signs and their disease can progress more slowly.


  1. Mitral Valve Disease in Dogs,https://vcahospitals.com/know-your-pet/mitral-valve-disease-in-dogs
  2. FDA Investigation into Potential Link between Certain Diets and Canine DCM,https://www.fda.gov/animal-veterinary/news-events/fda-investigation-potential-link-between-certain-diets-and-canine-dilated-cardiomyopathy

Meet The Author 

Dr. Erica Irish DVM


Erica has worked in the veterinary field since 2006, starting out as a veterinary technician before graduating from the UF College of Veterinary Medicine in 2013. As a general practitioner in an animal hospital, she has many interests and is especially interested in dermatology, cardiology, internal and integrative medicine.

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