Dog Health Articles - Heart Murmurs

It often comes as a surprise to owners to be told by the Vet that their dog has a heart murmur. The news often comes as a result of a routine check by the Vet when your dog  is in the clinic for something else. This is because vet will use a stethoscope to listen to the heart as part of his routine examination.

It can be distressing and worrying news especially as many dogs with heart murmurs appear normal to their owners and have no obvious symptoms of heart disease.

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 will 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. You should ask your Vet for this assessment.

Heart murmurs in puppies

If a heart murmur is present from birth or develops shortly after birth, it will probably be noticed by your veterinary surgeon at the time of  vaccinations.  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 and will generally disappear in the first year.

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.

Heart murmurs in adult dogs

This type of  heart murmur is usually due to heart disease that develops with age and was not present when a puppy.

In toy and small breeds of dog, a heart murmur may develop due to thickening and degeneration of the mitral valve in the heart, preventing it from closing properly and consequently leaking. The heart then has to work harder to compensate for this pumping inefficiency 

Large and giant breeds of dog typically do not suffer from mitral valve disease to the same extent and the usual heart disease affecting older larger dogs is called Dilated Cardiomyopathy or DCM.

The heart muscle has enlarged and can distort the mitral valve so that it cannot close properly. The resultant leak across the valve will cause a heart murmur.

How is a heart murmur treated?

If the heart murmur is caused by an underlying problem, the treatment will be based on the diagnosis, and may include a combination of specialized diets, medications and supportive care. Only a few congenital heart defects can be surgically corrected. Treatment and Care may well be required throughout your pet’s life.

Factors outside of the heart can cause murmurs

Not all murmurs are the result of a problem in the heart. Blood disorders, obesity, emaciation and parasitic conditions can create the conditions necessary to initiate a heart murmur.

What is the outlook?

The prognosis ranges depending on the cause of the murmur. If the murmur is not strong and the dog is a puppy the your vet will probably just keep and eye on the situation and offer no treatment.

The long-term prognosis for a dog with a murmur caused by congenital heart disease is extremely variable, depending on the specific type of defect that is present; if the defect can be surgically corrected the prognosis is very good. A dog with mitral valve problems can usually be managed with long-term medications.

The outlook for a dog with dilated cardiomyopathy varies – in the later stage the disease develops to ‘heart failure’ and then the prognosis will be grave though you may still enjoy your pet’s company for years to come. Treatment again includes a package of medication and dietary supplementation and control.