Canine Heart Disease: What You Need To Know

Vet listening to dog's heart with stethoscope
Cavalier King Charles Spaniels, Chihuahuas, Toy Poodles, Dachshunds and other small breeds can be prone to mitral valve disease.

Harper was unusually restless, and she had been coughing. The 9-year-old Cavalier King Charles Spaniel loved to eat grass — her owners thought that she might have a blade stuck in her throat. But when they noticed her rapid breathing, they became concerned. This looked like something more serious.

Heart disease is common in many dog breeds. It's been estimated that 7 to 8 million dogs in the United States have heart disease. It can be congenital, meaning the dog is born with it, or acquired later in life. Knowing whether your dog is prone to heart disease and what the signs are can help to save his life.

Types of Canine Heart Disease

Of those 8 million or so dogs with heart disease, approximately 75 to 80 percent have mitral valve disease, also known as chronic valvular disease. The mitral valve (which separates the left ventricle of the heart from the left atrium) degenerates and starts to leak. Instead of fully closing after the atrium contracts and pushes blood forward into the ventricle, it lets some blood leak back into the left atrium. That action, called regurgitation, causes the heart to work harder to pump blood. A similar thing can happen with the tricuspid valve on the right side of the heart, but that is less common.

Some people consider Cavaliers the poster dogs for mitral valve disease, the most common type of canine heart disease — but this breed isn't alone. Other breeds prone to mitral valve disease include Chihuahuas, Toy Poodles, Dachshunds and other small breeds, but larger breeds and mixes can be affected as well. Usually we see this condition in senior dogs, although Cavaliers typically develop it at an earlier age.

Labrador Retrievers, Old English Sheepdogs, Great Danes, German Shepherds and Irish Setters may be more prone to issues with the tricuspid valve.

Another type of heart disease seen in large dogs is dilated cardiomyopathy. This disease causes the heart muscle to weaken, making it less able to contract and pump blood. The heart becomes enlarged because it’s working too hard.

If you’re a gym rat, you know what happens when a muscle works hard: It gets big. For body builders, that’s a good thing. For the heart muscle, not so much.

The Telltale Heart Murmur

In all of these cases, dogs can progress to congestive heart failure. The classic sign of heart disease is often a murmur. Just like the buzz of a crowd at an exciting event, a murmur spreads the news that the heart’s operation may be off-kilter.

A normal heart sounds like this: lup dup, lup dup. A heart with a murmur sounds like this: lup shh dup.

If your dog is diagnosed with a murmur, your veterinarian may recommend diagnostic tests or refer you to a veterinary cardiologist or internal medicine specialist. A baseline exam can help establish the severity of your dog’s heart disease. He may show no signs and go on like that for years, or he may need to start on medication, depending on what the problem is with his heart and how well it’s working. That’s determined by his clinical signs, your veterinarian's physical exam findingings and diagnostics such as chest X-rays and an echocardiogram.