A heart murmur is one of several types of abnormal sounds your veterinarian can hear when listening to your pet’s heart with a stethoscope. Normally, two distinct sounds are heard when listening to the heart of a normal dog or cat. These are often described as “lub” and “dub”. When listening with a stethoscope one hears: Lub-dub…Lub-dub….Lub-dub. A murmur is an abnormal extra sound (which can sometimes drown out the normal sounds). Murmurs most commonly occur between the “lub” and the “dub” and have a “shooshing” or “whooshing” quality.
Hearing a murmur is only a hint that something may be wrong, not a final diagnosis. Hearing a murmur is reason to consider more discussion and tests to determine the cause of the murmur (the diagnosis). Knowing the diagnosis and severity of the cause of the murmur allows your veterinarian to provide you with an educated guess (prognosis) regarding how this heart problem may affect your pet in the future. Hearing a murmur is not a reason to panic. Many dogs and cats with murmurs live normal lives and never need any treatment for heart disease. But the only way to know for certain is to work with your veterinarian to determine the cause and severity of the cause of the murmur.
What causes a heart murmur?
The short answer to this question is “turbulent blood flow.” Like the water in a calm river or stream, blood flowing normally flows through the heart with laminar flow – that is, it is smooth and undisturbed. And like a river or stream, narrowing or other causes of more rapid flow will disrupt this smooth laminar flow. In a river the turbulent rapids emit sounds much louder and less tranquil than the calmer sections of river. In the heart we hear this turbulence as a murmur.
The most common murmurs in dogs are associated with leaky mitral valves. Degenerative valve disease accounts for about 75% of cardiovascular disease in dogs.
In other cases, the turbulence develops because there is a “hole in the heart” between two chambers or two arteries that are not normally connected.
Another cause is a narrowing (stenosis) within a chamber or vessel through which the blood has to “squeeze” through, like water through a pinched hose.
Finally, turbulence can be heard when the blood is too “thin” (anemia) or even when a patient is very excited causing the heart to pump faster and harder than normal.
What is a benign or “innocent” murmur?
Some heart murmurs are called benign (or innocent or physiological), meaning there is no apparent heart disease that explains the murmur. These murmurs are often seen in puppies, and can occur in cats of any age. They are uncommon in adult dogs. Benign murmurs are usually soft (rather than loud), and can be intermittent. Benign puppy murmurs will generally disappear by 12 to 15 weeks of age. Murmurs associated with anemia or excitement are also considered benign murmurs.
My pet’s murmur has a “grade.” What does this mean?
Murmur grading is simply your veterinarian’s way of describing the loudness of a murmur. There are six murmur grades. The grade or loudness of the murmur is only sometimes related to the severity of the heart abnormality causing it.
What should I do if my pet has a murmur?
Dogs
In many cases, a veterinarian will be able to determine the likely cause of a murmur in a dog just by an x-ray. In some cases, no additional testing will be deemed necessary. However, in other cases it is best to confirm the cause of the murmur as well as the severity of the condition that is causing the murmur. This will give you the best idea of what to expect in the future.
Cats
In cats, benign murmurs can sound exactly like murmurs in a cat with serious heart disease. In fact up to 35% of cats with heart disease do not have any audible abnormalities on examination.
In both dogs and cats, your veterinarian may elect to perform chest radiographs (x-rays), an echocardiogram (ultrasound of the heart), or other imaging studies, or to refer your pet to a specialist for these procedures. The tests that are performed depend on the individual case.
How is a murmur treated?
The murmur itself is not treated. The underlying cause of the murmur may or may not be treated – this depends on the cause, severity, and other circumstances (age, well-being of the pet, cost of treatment etc). Your veterinarian is best suited to discuss specific treatment options with you.