Understanding Heart Murmur in Dogs

Understanding Heart Murmur in Dogs


Your dog’s heart functions just like a human heart, and they can experience the same heart problems we do. A heart murmur in dogs is often discovered with a stethoscope during a routine physical examination at the vet. Dogs with heart murmurs may not display outward symptoms, and pet parents may be totally unaware that the murmur even exists.

You don’t have to be a veterinarian to figure out that the function of your pet’s heart is important! The diagnosis can be very alarming, especially when the vet starts using words like heart disease, echocardiogram, x-ray, congestive heart failure, and mitral valves. What does it all mean, and how serious is it?

Although a heart murmur can be very serious, many times they’re not. Here’s what pet parents need to know about the causes, diagnosis, and treatment of heart murmurs in dogs.

Heart Murmur in Dogs: What Does it Mean?

We all know that the heart is responsible for pumping blood throughout the body, whether you’re human or animal. You’ve probably even heard your dog’s heart sounds at some point during cuddle time, and you know that its steady beat keeps him alive.

When this steady rhythm becomes uneven and blood flow is irregular, it causes abnormal heart sounds that your vet’s trained ear can hear with a stethoscope. This irregular rhythm and abnormal sound in your dog’s heart is called a heart murmur.

Classifying Heart Murmurs in Dogs

Heart murmurs in dogs have several different classifications. To help you understand the seriousness of your dog’s heart murmur diagnosis, you need to understand the different types, grades, and configurations used to classify them.

Understanding the Different Types of Heart Murmurs That Occur in Dogs

Heart murmurs are classified into three different types: diastolic, systolic and continuous.

  • Diastolic murmurs occur when the dog’s heart relaxes in between beats.
  • Systolic murmurs happen when the dog’s heart muscle is contracting.
  • Continuous murmurs occur throughout the entire heartbeat cycle.

Determining which type of murmur your dog has will help your vet diagnose the underlying cause of the murmur.

How Heart Murmurs Are Graded

Determining the grade of your dog’s heart murmur will also help your vet diagnose the cause and determine the best course of treatment. Heart murmurs in dogs are graded on a scale of one to six according to the loudness of the heart sounds, with six being the most serious.

  1. At this level, the murmur is barely detectable, even with a stethoscope. This grade of murmur is very unlikely to cause issues for your dog.
  2. Grade two murmurs are still very soft but can be heard with a stethoscope. They are usually not very serious.
  3. A grade three heart murmur and is more likely to lead to serious issues.
  4. A grade four murmur is quite loud and can be heard on both sides of the chest.
  5. Grade five murmurs are very loud and might be felt with a hand against the dog’s chest.
  6. A grade six is the most severe heart murmur. It is the loudest and can easily be felt through the chest wall.

Configurations of Heart Murmurs in Dogs

Heart murmurs in dogs are also classified into four different configurations.

  • plateau murmur has uniform loudness and is often associated with insufficiency in the aortic valve.
  • Crescendo-decrescendo murmurs fluctuate in loudness and are often associated with heart conditions like aortic and pulmonic stenosis.
  • Decrescendo heart murmurs are loud and then become quieter. They are most common when the dog has an aortic valve insufficiency or possibly a ventricular septal defect.
  • Continuous, or machinery quality, murmurs are usually associated with a congenital heart defect called patent ductus arteriosus (PDA).

All of these different classifications and cardiology terms can be very confusing, so don’t hesitate to ask your vet any questions you may have about your dog’s specific condition.

Causes of Heart Murmurs in Dogs

Once a veterinary cardiologist has determined what kind of heart murmur your dog has, he will be able to determine the cause and make recommendations on what to do next. Heart murmurs can be caused by a variety of heart defects and diseases. In addition to determining the type of murmur, your dog’s breed, age and test results will be used to diagnose the cause of the heart murmur.

In general, the most likely cause of heart murmurs in dogs falls into one of these three categories of heart valve and blood flow disturbances.

  • Regurgitant flow
  • Obstruction, dilated vessels, or diseased valves
  • Abnormal valves or vibrations

Different types of illnesses can also cause a heart murmur in dogs.

Causes of Systolic Murmurs

Systolic murmurs are the most common type of heart murmur in dogs. They are usually caused by pulmonic stenosis or subaortic stenosis, which happens when the blood vessels are narrow and blood flow is obstructed. Other causes include heartworm disease, hyperthyroidism, and other types of heart disease.

Causes of Diastolic Murmurs

Diastolic murmurs in dogs are quite rare. Aortic insufficiency is the most common cause. It happens when the aortic valve doesn’t close correctly, allowing it to leak. This type of murmur can also be caused by aortic and pulmonic valve endocarditis.

Causes of Continuous Murmurs

Continuous murmurs can be caused by PDA and aortic regurgitation with a ventricular septal defect or aortic stenosis.

Innocent Heart Murmurs in Dogs

While a diagnosis of heart murmur can be scary, there are some that are classified as innocent murmurs. These murmurs usually resolve on their own over time, and they’re not considered serious. They generally occur in younger dogs and are classified a grade three or lower.

Treatment of Heart Murmurs in Dogs

The first thing you need to know is the heart murmur itself isn’t actually what’s treated. It’s the cardiac disease itself and its symptoms that are treated, depending on the diagnosis. For example, if your dog’s heart murmur was caused by hyperthyroidism or heartworm disease, the treatment will be entirely from a dog who’s murmur is caused by congestive heart failure. If the dog is young, no treatment may be recommended at all, in hopes it will resolve on its own.

So, What’s the Bottom Line?

Although a heart murmur diagnosis in dogs can be serious, in many cases, the cause is treatable or may even resolve on its own. If your dog is older, the condition can be scary, but the sooner it’s addressed, the more likely a positive outcome. And that’s why regular wellness checkups are so important!

Anna Marston
Anna is a full-time veterinary technician with more than 20 years of experience in the pet care industry. She resides in Upstate New York with her hubby, daughter, and a menagerie of fur-babies.

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