What is a heart murmur? (Dr. Danowitz)

When you bring your pets in for their annual physical examination, chances are, at some point or another, you may have heard one of our veterinarians comment, “Fluffy has a heart murmur today”. While some animals with heart murmurs have serious clinical signs such as exercise intolerance, coughing, and difficulty breathing, a great number of pets, just as people, have heart murmurs but feel and act completely normal. My own dog, Janey, has a heart murmur, which I discovered when she was three years old. So what does that actually mean?

A heart murmur is simply an “abnormal sound” heard with a stethoscope. The normal heart of a dog or cat (or human, for that matter) can be characterized as a ‘LUB…DUB’. With an animal that has a heart murmur, the sound is more along the lines of ‘LUB..WHHOOOOOSSHH..DUB’.

Example of normal heart sound:

Example of heart murmur:

This sound is an indication that there is an interruption in the normal blood flow in the heart, which can happen for many reasons. Some potential causes of heart murmurs include: valve problems (i.e. leaky mitral valve in humans), congenital heart defects, and problems with the thickness and function of the heart muscle. We can also see “innocent heart murmurs” in young puppies and kittens, as well as in animals that have other underlying health problems such as anemia and hyperthyroidism.

How do you know what a heart murmur means to your beloved pet? There are several tests that can be performed to determine the cause of the heart murmur and the severity of any underlying heart disease. The three most common tests performed at our hospital are: chest radiographs (X-Rays), blood pressure, and a cardiac ultrasound (echocardiogram).

Chest X-Rays are useful for multiple reasons. The X-Ray allows the veterinarian to assess heart size as well as to evaluate the lung fields around the heart. When heart disease is very advanced, fluid can often form in or around the lungs; this condition is referred to as congestive heart failure, and is diagnosed with X-Rays. A normal dog chest X-Ray (left) compared to a pet in heart failure (right) can be visualized below:

Blood pressure is also important in animals with cardiac conditions. Animals with high blood pressure are often placed on medications, much like humans, to control their hypertension. If untreated, high blood pressure can cause certain medical conditions to progress more rapidly. In the animal hospital, it can often tricky to get accurate blood pressure measurements, as our patients are often a little stressed.

A cardiac ultrasound, or echocardiogram, is a way to see inside the heart at the four chambers, valves, and heart muscle. With this test we can acquire loads of information regarding muscle thickness and function, valve thickness, chamber dilation, obstructions to blood flow and other things as well. Measurements are taken of your pet’s heart components, and then compared to the normal measurements for a dog or cat of your pet’s size. An example of a cardiac ultrasound can be seen below:

The results of these three tests are used to determine whether or not there is substantial heart disease in an animal, and whether any medication is indicated to help them. Cardiac medications are aimed to slow the progression of heart disease and control the symptoms, but cannot “cure” any existing heart problem. It is for this reason that early detection and diagnosis of heart disease can make a big difference in long-term outcome.

I mentioned earlier that my own dog, Janey, has a low-grade heart murmur. I recently ran the three tests mentioned above, and her heart disease is mild enough that she does not yet require any medication. Since heart disease typically worsens with age, I will recheck her chest X-Rays, blood pressure, and cardiac ultrasound each year to monitor her progression.

Dr. Danowitz

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