Should You Worry About Heart Murmurs in Dogs?

When you are told that your dog has a heart murmur, it can be a really distressing time. However, there are many causes of a heart murmur in dogs. While it could be a symptom of a disease that requires treatment, it could also be something that ends up being really quite insignificant and can disappears over time.

What Are Heart Murmurs in Dogs?

Dog’s hearts beat at a regular pace as blood is pumped through their bodies. When a veterinarian uses a stethoscope to listen to your dog’s heart, they will hear the sounds made by the blood rushing through it from the opening and closing of the valves. When you are told that your dog has a heart murmur, that is because the vet can hear extra or unusual sounds caused by a disturbance in the blood flow.

Symptoms of a Heart Murmur

Not all heart murmurs come with additional symptoms. The main symptoms usually consist of panting and coughing. However, when the murmur is caused by heart disease, you may also see:

  • Exercise intolerance: your dog no longer runs around as much they used to, and when they do, it then takes them much longer to recover.
  • Lethargy or weakness: this might show as your dog not being keen to join in games they used to enjoy or not being as steady on their legs as they were. This may develop into your dog fainting or even collapsing.

Causes of a Heart Murmur in Dogs

There are many different causes of heart murmurs, including:


The valves in the heart act as non-return valves, so that means that blood can only flow in one direction. But if a valve becomes faulty, there can be a squirt of blood through the gaps in the valve with each heartbeat, causing the sound of the heart murmur. The most common cause of this in older dogs is a condition called myxomatous mitral valve disease.

Narrowed Valves

If a heart valve is very narrow, then the blood flow being pumped through it is squirting at a much higher pressure than usual.

Holes in the Heart

If your dog has a hole in their heart, then the sound of the murmur comes from the blood squirting through the hole.

Murmurs Associated With Illness

There are several different conditions that can cause a heart murmur in dogs:

  • Anemia which results in thinning of the blood, making the heart pump faster than normal
  • Heartworm, causing a narrowing of the blood vessel, resulting in obstruction of the blood flow
  • Hyperthyroidism, causing the heart to enlarge and thicken
  • Endocarditis caused by an infection of the heart valves (this happens when bacteria from other parts of your dog’s body, such as from dental disease, spread through the bloodstream and then become lodged in your dog’s heart)

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Diagnosis of a Heart Murmur

Once you vet suspects that your dog may have a heart murmur, they will then listen more closely to establish which one of the following three categories it fits into:

  • Systolic: a murmur occurs when the heart contracts
  • Diastolic: occurs in between beats
  • Continuous: occurs throughout

Then, they may also grade it on a scale of loudness. This is because some murmurs can be very quiet, while others can be loud enough to hear without even needing a stethoscope. Grades 1, 2 and 3 are the quietest ones. Now, these often occur in puppies and are known as an “innocent murmur”. These usually cause no problems for puppies and have disappeared before they are 4 months old.

The louder heart murmurs (grades 4, 5 and 6) will need evaluation by a cardiologist who will carry out an echocardiogram, which allows them to see the structure and function of the heart in real time. Your dog will not usually need to be sedated for this procedure as they just need to lay quietly for around 20 minutes while the veterinary technicians gently hold them in place.

Treatment Plans for a Heart Murmur

While the heart murmur itself cannot be treated, the symptoms and problems of the condition causing the murmur usually can. With so many different causes of the problem, the treatment can vary hugely. Heartworm, for example, is generally treated with medication, but extreme cases may require surgery.

In some cases, especially with the mild murmurs often seen in young dogs, it may disappear all on its own with the need for any treatment.

Can Heart Murmurs Be Prevented?

Just as with treatment, the heart murmur itself cannot be prevented, but the condition which caused it might be preventable. So, you should ensure that your dog receives their heartworm preventatives and brush your dog’s teeth regularly to prevent bacteria from traveling to the heart.

Breeders can also play their part in ensuring that they only breed from dogs who are free from the genetic conditions that cause heart murmurs. These include:

  • Myxomatous mitral valve degeneration (MMVD), which is seen in several different breeds including the Cavalier King Charles Spaniel, Cocker Spaniel and the Chihuahua.
  • Dilated cardiomyopathy (DCM), which also affects several breeds, including the Doberman Pinscher, Great Dane and the Boxer.