It is scary when your dog has been diagnosed with a heart murmur. Heart murmurs affect around 60% of dogs over the age of 5 years old.  

What is a Heart Murmur?

When your vet is listening to your dog’s heart through a stethoscope, they can hear the rhythmical lub-dub. This sound is made from the normal opening and closing of the heart valves (explained further later on). When there is any turbulence of blood flow, the lub-dub is replaced by a swoosh noise – swoosh-dub, swoosh-swoosh, etc. This is what we call a heart murmur.

It is important to know that a heart murmur is not a name for a disease, but a name for what we hear – and heart murmurs can be caused by many different conditions.

What is the Grading Scale for Heart Murmurs in Dogs?

Not all heart murmurs sound the same. Some have different intensity, location and time. The intensity of the murmur does not usually correlate with the severity of heart disease. Veterinarians grade the intensity of the heart murmur into 6 different grades. 

  • Grade I—barely audible murmur
  • Grade II—soft murmur
  • Grade III—intermediate loudness murmur; most murmurs which are related to the mechanics of blood circulation are at least grade III
  • Grade IV—loud murmur 
  • Grade V—very loud murmur
  • Grade VI—very loud murmur with a vibration strong enough to be felt through the animal’s chest wall

What causes Heart murmur in Dogs?

As noted, a heart murmur is caused by turbulence blood flow within the heart. A heart murmur can also be classified as an innocent/physiologic murmur. An innocent heart murmur has no impact on the dog’s health. This most often occurs in young puppies and they eventually outgrow the murmur by around 5 months of age. If your vet has detected an innocent heart murmur in your young puppy, your vet will most likely recommend listening to the heart again when your puppy is 4-5 months of age. If the heart murmur is still present, a cardiac work up will be warranted. 

More commonly, heart murmurs in older dogs are caused by cardiac disease (pathological murmurs) or a problem outside the heart. 

What kind of cardiac disease causes a heart murmur?

A heart murmur caused by cardiac disease can be either congenital or acquired

Congenital heart diseases in puppies are hereditary and include diseases such as:

  • Patent ductus arteriosis (PDA)
  • Pulmonic stenosis
  • Sub-aortic stenosis 

Acquired heart diseases are caused by cardiac diseases and develops in adult dogs. This includes:

  • Myxomatous Mitral Valve Degeneration also known as Mitral insufficiency, Mitral regurgitation or MMVD. This is a heritable disease seen in breeds including the Cavalier King Charles Spaniel, Cocker spaniel, Chihuahua, Miniature Poodle, Boston terrier, and Miniature Schnauzer.
  • Dilated Cardiomyopathy also known as DCM. This is a heritable disease seen in breeds including the Doberman Pinscher, Great Dane, Boxer, and the Cocker Spaniel. 
  • Endocarditis – This infection of the heart valves occurs when bacteria from other parts of your dog’s body such as dental disease, spreads through the bloodstream and lodges in your dog’s heart.

How can we diagnose a heart murmur?

If your vet detects a heart murmur during your dog’s physical exam, certain tests may be recommended depending on the grading, location and time of murmur.

The first test that you vet may recommend to investigate your dog’s heart murmur is an echocardiogram. This is an ultrasound of the heart performed by a specialist. An echocardiogram is extremely valuable because it will give us a diagnosis of what is causing the heart murmur. It will also examine the health of the heart valves, measure the blood pressure to the lungs and examine any secondary changes to the heart including abnormal thickness.


A chest x-ray may also be recommended to look at the chest. A chest x-ray provides us valuable information about the chest cavity. This includes looking at the lungs to see if there is any fluid if the heart is putting any pressure on the windpipe and to measure how big the heart in the chest cavity. 


What are the signs of a heart murmur?

There are NO signs if we detect the heart murmur early. Every year your vet will listen to your furbaby’s heart for any murmurs during their yearly health check ups. 

Is my dog in heart failure?

Heart murmurs with pathological heart diseases usually progress into congestive heart failure. This is a serious condition and can be fatal. Commonly, dogs that are in heart failure will have an accumulation of fluids in their lungs. Dogs with heart failure may also have a cough, exercise intolerance or difficulty breathing.   

Signs of congestive heart failure:

  • Lethargy
  • Fainting
  • Collapsing
  • Coughing 
  • Gagging
  • Trouble breathing
  • Exercise intolerance
  • Reduced appetite
  • Swelling in the abdomen
  • Muscle loss

Coughing from heart diseases can be caused by two reasons. 

  • Dilation of the heart size which leads to compression of the windpipe
  • Potential backflow of blood which leads to fluid buildup in the lungs

Coughing can also be a sign of respiratory diseases such as bronchitis, allergies, pneumonia, asthma or kennel cough. Hence, it is very important for your vet to perform a thorough workup. 

How do you treat a Heart Murmur?

Treatment for your dog’s heart murmur will depend on the underlying cause. An innocent murmur will not require any treatment, but regular monitoring of your dog’s heart condition is recommended to ensure no other problems develop. 

A heart murmur caused by cardiac disease may require medication(s) and a specialised diet. Your dog will need regular vet visit for a routine monitoring every 6 months. This may include a repeat echogram and/or x-rays depending on your dog’s conditions. 

Your veterinarian will advise you on the best course to treat and monitor your dog’s heart murmur. 

What is the prognosis of a Heart Murmur?

Your veterinarian will discuss the prognosis and treatment options for your dog as each case is specific and different. In all cases, ongoing monitoring and regular diagnostic testing are needed to monitor the heart murmur.

At My Vet Animal Hospital, we work closely with specialists in Small Animal Medicine and advanced training in Cardiology. We are able to organise a specialist to come to our clinic for an echocardiogram, rather than you travelling to a specialist hospital. We also offer diagnostic x-rays and blood testing in house for immediate results. If your dog needs special heart medication and doesn’t like tablets, we can also offer personalised compounded medicine with added flavour including chicken, beef or fish. This is our way to ensure your dog has an accurate course of diagnosis, access to gold-standard monitoring tests and the best treatment. 

If you have any concerns about your dog’s heart, please do not hesitate to reach out to us!

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