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Are Dog Heart Murmurs Genetic? Vet-Reviewed Types, Grades & FAQ

Kit Copson

By Kit Copson

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Reviewed & Fact-Checked By

Dr. Lorna Whittemore

MRCVS (Veterinarian)

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When your dog is diagnosed with something—especially something heart-related—it can be a worrying time. The first thing to know if your dog has been diagnosed with a heart murmur is that there are several different types of heart murmurs. Some are congenital heart defects present at birth, and some of these are genetic, while others are not. Genetic heart problems can also show up later in life such as dilated cardiomyopathy, (DCM). Heart murmurs also vary in severity, with some requiring no treatment at all.

In this post, we aim to give you an insight into the facts about heart murmurs in dogs—what causes them, symptoms to look out for, and how they are treated.

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What Are Heart Murmurs in Dogs?

If a vet listens to your dog’s heart with a stethoscope and hears an abnormal sound, this is a heart murmur. When the blood flow to, or through the heart is disrupted or otherwise turbulent, it causes vibrations. These vibrations are what cause abnormal heart sounds. Heart murmurs are usually a whooshing sound and are graded to reflect the degree of loudness but not necessarily severity.

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Grades of Heart Murmur

  • Grade one: This is the quietest type of heart murmur. It is barely audible when a vet listens with a stethoscope.
  • Grade two: This type of heart murmur is soft but clearly audible with a stethoscope.
  • Grade three: This is what we could call the “middle-ground” murmur. It’s very easily audible and louder than a grade two.
  • Grade four: Grade four murmurs are loud and heard on both sides of the chest.
  • Grade five: Very loud and vibration can be felt when the chest is touched with a hand.
  • Grade six: The loudest possible heart murmur, vibration can be felt and the murmur can be heard with the stethoscope not touching the chest wall.

Types of Heart Murmur

The three types of heart murmur are systolic, diastolic, and continuous, which reflects the timing in the heartbeat cycle that they are heard in. Systolic murmurs (with the pulse) occur when the heart contracts whereas diastolic murmurs (after the pulse) are heard as the heart relaxes to re-fill. Continuous murmurs are heard throughout the heartbeat phase and are usually caused by the ductus arteriosus (a blood vessel) not closing after birth. This condition is called patent ductus arteriosus (PDA).

Systolic murmurs are the most common and have the longest list of causes, whereas diastolic murmurs are much less common. With continuous murmurs, patent ductus arteriosus—the most frequent cause—is congenital and often inherited.

Finding out the level of severity of the problem causing the heart murmur will need some investigation . Vets will take into account the dog’s overall health and try to determine if there is an underlying, serious condition causing the murmur. Blood tests, ECG and ultrasound may be needed. Not all heart murmurs signify heart disease, for example puppies up to the age of 20 weeks may have an innocent murmur that gradually gets quieter with each vet visit and is usually gone by 5 months. However, many do signify disease or malformation and will require long-term treatments.

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What Causes Heart Murmurs in Dogs?

Heart murmurs in dogs can be caused by congenital heart defects, diseases, or what’s known as “extracardiac” conditions. Extracardiac conditions are those that are not primarily heart-related.

Structural heart disease is one of the congenital causes of heart murmurs. This means that there are defects in the structure of the heart from birth that cause interference with normal blood flow. Hereditary heart diseases in dogs include pulmonic stenosis, subaortic stenosis, and patent ductus arteriosus.

Examples of extracardiac conditions that can cause heart murmurs are anemia, heartworm, hyperthyroidism (overactive thyroid), hypoproteinemia (low protein levels), being obese or emaciated, pregnancy, and infection.

What Are the Symptoms of Heart Murmurs?

Symptoms can vary depending on the condition causing the murmur. Some dogs, especially those with low-grade heart murmurs, may show no symptoms whatsoever; others may have a list of complaints such as those below.

Dogs with a heart condition may display symptoms including:
  • weakness
  • lethargy
  • fainting or collapsing
  • a persistent cough
  • not wanting to or unable exercise
  • pale gums
  • Ascities-bloating caused by fluid build up in the abdominal cavity
  • excessive panting when resting
  • loss of appetite.

As the symptoms can vary depending on the condition, it’s a good idea to be vigilant for any general changes in your dog’s physical health or demeanor. If in doubt, speak to your vet.

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Can Heart Murmurs in Dogs Be Treated?

When a vet treats a heart murmur, they treat the condition causing it rather than the heart murmur itself. As there are many possible causes for heart murmurs, treatment plans will vary. Some dogs may need medication, a change in diet, and in some cases, surgery. “Innocent” heart murmurs—ones that do not harm the dog’s overall health— don’t require any treatment.

Vets will recommend regular check-ups on dogs with heart murmurs to monitor for progression and overall health.

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Final Thoughts

A heart murmur is not so much a stand-alone condition as it is a symptom of another condition. While it sounds scary, sometimes a heart murmur diagnosis can be positive in that it means the underlying condition causing it will be treated sooner rather than later.

If you’re concerned that your dog may have a condition that’s causing a heart murmur, have a chat with your vet. They will be able to assess the situation and make a decision on whether or not treatment is necessary.

Featured Image Credit: Ermolaev Alexander, Shutterstock

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