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What is a Heart Murmur in Dogs?

What You Need to Know About Your Dog's Telltale Heart Sounds

By Sam Bourne. December 09, 2013 | See Comments

  • expert or vet photo
    vet verified

    PetCareRx Staff Veterinarian

    DVM

Beagle with a stethoscope

The heart is a crucial organ, so anytime something seems off, it can be cause for worry. While it can be indicative of many different things, a heart murmur in dogs can range from being innocent and non-harmful to symptomatic of a potentially life threatening ailment.

The heart is the very definition of a vital organ, so when it starts making weird noises, people tend to grow concerned. A heart murmur in dogs can present as strange whooshing noises. It can range from being an innocuous sound, often resulting from rapid growth (as is often found in large breed puppies), to a sign of something more dire.

There are a number of different causes for a heart murmur in dogs, and the cause can often be discerned based on the loudness and frequency of the murmur. To better understand what is happening, here is what you need to know about heart murmurs.

What are heart murmurs?

A heart murmur is a disturbance in the blood flow through the heart, resulting in an audible noise. Heart murmurs range in how loud they are, as well as where they fall in the heartbeat cycle; systolic heart murmurs occur when the heart is contracting and diastolic heart murmurs occur when the heart relaxes. There are also continuous heart murmurs and to-and-fro murmurs, which happen across both the relaxed and contracted heart cycles.

How are murmurs categorized?

Heart murmurs exist on a graded scale, based on how loud the murmur is.

  • Grade I -- almost undetectable
  • Grade II -- soft, but detectable with a stethoscope
  • Grade III -- intermediate loudness
  • Grade IV -- loud murmur easily heard throughout the chest
  • Grade V -- very loud, almost not requiring a stethoscope
  • Grade VI -- very loud, able to feel the murmur through the chest wall

Depending on the grade of your dog’s heart murmur, your vet may ask you a series of questions in order to assess what the cause of the sound is, and whether it requires immediate treatment.

What are the causes of heart murmurs?

Heart murmurs in dogs can be caused by a number of different factors. Occasionally, dogs will have a heart murmur that is entirely innocent, caused by physiological conditions that have no impact on your dog’s health. These murmurs are typically low grade (I-II), and require no treatment.

A structural heart problem can often cause a heart murmur, such as a leaky heart valve, a thinning or thickening of the valve, or a hole between chambers of the heart. Structural problems are either congenital (from birth) or acquired.

In some cases, the cause of the heart murmur is outside the heart itself, known as an extracardiac problem. If your dog is dealing with anemia (low red blood cell count), hypoproteinemia (low protein levels), a fever, pregnancy, or obesity, these conditions can result in a heart murmur.

How to detect a heart murmur

Since most of us are not walking around with stethoscopes, here are a few more obvious symptoms of heart murmurs. If you notice that your dog is suffering from any of the following, take them to the vet.

How to diagnose the cause behind a heart murmur

Oftentimes, if a heart murmur is detected, your vet will recommend that your dog undergo an x-ray, electrocardiogram, or an ultrasound to get a better look at what the heart is actually doing. From these images, your vet should be able to tell you what the specific cause of the murmur is, and depending on the cause, provide a diagnosis and suggest the best method for treatment.

Treatment of heart murmurs

What gets treated is the cause of the murmur, not the murmur itself, so depending on why your dog’s heart is making noise, your treatment options can vary.

For dogs with a physiological heart murmur, oftentimes nothing is done, as the cause of the murmur generally corrects itself over time.

For heart murmurs caused by structural problems, like a leaky valve or a hole between chambers, surgery could be an option, along with specialized diets, medication, and supportive care to help correct the malformation.

Extracardiac problems, or heart murmurs that are caused by factors outside the heart, can be treated in a number of different ways depending on the condition. Often the result of anemia, hypoproteinemia, parasites, or bacterial infection, the treatment of the specific underlying condition is the first step to correcting the heart murmur.

More on Heart Health

Heart Disease in Dogs and Cats
Dogs with Congestive Heart Failure
4 Common Causes of Heart Failure in Dogs

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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