My dog has a heart murmur. What does this mean?

Whenever the word ‘heart’ is mentioned we always fear the worst. Heart murmurs are a relatively common problem in dogs and in this article, Heart Expert Nuala Summerfield explains what a heart murmur is and clarifies that not all murmurs in dogs are a sign of a more serious problem.

What is a heart murmur?

heart murmurs in dogs

Your vet will use a stethoscope to listen to all areas of the heart

A heart murmur is a specific sound detected when listening to the heart with a stethoscope. This sound is a result of the blood flowing faster than normal within the heart itself or in one of the two major arteries leaving the heart (the aorta and pulmonary artery). Instead of the normal Lubb Dupp, an additional sound is present that can vary from a mild pshhh to a loud whoosh!

Your vet may use a grading system from 1 to 6 to describe how loud the murmur is e.g. a grade 1 murmur is very soft and a grade 6 murmur is very loud.

Heart murmurs in dogs can develop at any stage of their life. However, the significance of the heart murmur can be very different depending on the age at which the murmur is first detected.

My dog seems normal to me but my vet has detected a heart murmur. Is this possible?

It often comes as a surprise to owners to be told that their dog has a heart murmur. Many dogs with heart murmurs seem normal to their owners and have no obvious symptoms of heart disease. However, it is important to remember that the presence of a heart murmur is just an indication that there may be underlying heart disease. In itself the heart murmur is not a diagnosis. This is why further investigations such as x-rays, ECG or an ultrasound scan of the heart (also referred to as an echocardiogram or ‘echo’) may be required.

pet lifesavers ad HMP

If your dog has had a heart murmur detected but is not showing symptoms of heart disease, it is possible that the heart disease may not yet have developed significantly enough to affect the normal functioning of the heart. However, this situation can change and cardiac symptoms can develop rapidly. By gaining as much information as possible about your dog’s heart, you and your veterinary surgeon will be in the best position to recognise early symptoms of heart disease should they occur. This is very important as it means that appropriate treatment to assist heart function can be started promptly if and when it is required.

Heart murmurs in puppies

heart disease in puppies

Innocent ‘flow murmurs’ are the most common type of heart murmur detected in puppies. These disappear by 5 months of age

If a heart murmur is present from birth or develops shortly after birth, it will probably be detected by your veterinary surgeon at the first or second vaccinations. In puppies, there are two major types of heart murmurs. The most common type is called an innocent “flow murmur”. This type of murmur is soft (typically a grade 2 or softer) and is not caused by underlying heart disease. An innocent flow murmur typically disappears by 4-5 months of age.

However if a puppy has a loud murmur (grade 3 or louder), or if the heart murmur is still easily heard with a stethoscope after 4-5 months of age, the likelihood of an underlying congenital heart problem (i.e. heart disease that the puppy was born with) becomes much higher. Examples of congenital heart problems in dogs are patent ductus arteriosus, aortic stenosis and pulmonic stenosis. Interestingly, some types of congenital heart disease in puppies have very characteristic sounding heart murmurs.

The thought of your puppy having congenital heart disease is understandably extremely worrying, but it is important to remember that not all types of congenital heart disease will affect your puppy’s’ life expectancy and quality of life. If congenital heart disease is suspected, your vet will almost certainly want you to see a specialist for further assessment.

Heart murmurs in adult dogs

A heart murmur can also develop suddenly in an adult dog that has had no prior history of a heart murmur as a puppy. This type of heart murmur is typically due to heart disease that develops with age (i.e. the heart disease was not present at birth).

In toy and small breeds of dog, a heart murmur may develop in middle-aged to older dogs due to an age-related thickening and degeneration of one of the valves in the heart called the mitral valve. This thickening of the valve prevents it from closing properly and as a result it starts to leak. This leakage of blood across the thickened mitral valve results in a heart murmur. The disease which causes the thickening and distortion of the mitral valve is known as myxomatous mitral valve disease and we will talk about this common condition some more in future articles.

dilated cardiomyopathy in dogs

Disease of the heart muscle (cardiomyopathy) most commonly affects larger and giant breeds of dog

Large and giant breeds of dog typically do not suffer from myxomatous mitral valve disease to the same extent as smaller dogs. The more common type of heart disease affecting middle-aged and older larger dogs is called Dilated Cardiomyopathy. This type of heart disease causes the heart muscle to become weak and flabby. Although dilated cardiomyopathy does not directly damage the heart valves, the changes in the heart muscle can stretch and distort the mitral valve so that it cannot close properly. The resultant leak across the valve will cause a heart murmur.


What is the best way to investigate a heart murmur?

The best way to investigate the cause of the heart murmur is with an ultrasound examination of the heart (an echocardiogram). Once the cardiologist has evaluated your pet, they will be able to give you as the owner, as well as your veterinary surgeon, all the necessary information about the health of your dog’s heart and to advise you on what treatment, if any, is necessary.