What is a heart murmur?
A heart murmur is an abnormal heart sound, usually heard by listening to the heart with a stethoscope.
A heart murmur is caused by turbulent blood flow within the heart. Sometimes a murmur is determined to be “innocent” or “physiologic,” while other times the murmur is determined to be pathologic or caused by disease. Pathologic heart murmurs can be caused by a structural problem within the heart (i.e., cardiac disease), or can be due to an extracardiac problem (i.e., not caused by heart disease).
What conditions cause heart murmurs in dogs?
There is a wide range of conditions and diseases that can cause a heart murmur in dogs.
Most commonly, heart murmurs in small dogs are caused by a leaky mitral valve (the heart valve in between the left atrium and left ventricle). The mitral valve allows blood to flow from the left atrium to the left ventricle but does not allow for blood to flow back into the left atrium. Sometimes as a dog ages the valve degenerates which causes blood to leak backward. This condition is known as chronic valve disease, degenerative mitral valve disease, or endocardiosis.
In larger breed dogs, heart murmurs are often caused by a disease called dilated cardiomyopathy (with a subsequent leaky mitral valve). Dilated cardiomyopathy is a disease that causes the muscles in the pumping chamber of the heart to become weakened and decrease the contraction strength of the heart.
While these are common culprits of heart murmurs, there is a range of other issues that can cause a murmur to occur. Your vet will be able to run the proper diagnostic tests to properly assess your pets heart and determine the cause of the heart murmur.
What causes a heart murmur in Dogs?
The cause of a heart murmur varies. Some murmurs are determined to be “innocent” or “physiologic,” while other times, they are determined to be pathologic or caused by a disease, such as a structural problem within the heart (cardiac disease). Murmurs can also be due to a problem that is “extra-cardiac,” meaning they are not caused by heart disease.
Dog Heart Murmur! 3 Vet Tips
Not so many years ago, a person with a happy, healthy dog with a loud heart murmur would be advised by their veterinarian to wait and start treatment only once signs of heart failure developed.
This wait-and-see approach to dogs with heart murmurs was accepted wisdom until a few years ago.
Back then, we all believed starting drugs too early, before the dog developed a cough or struggled to exercise, would reduce the medication’s effectiveness when the dog really needed it.