Heart Murmurs in Pets
When veterinarians talk about heart sounds, they are referring to those that can be heard with a stethoscope during a physical examination.
A normal heart has two distinct sounds, described phonetically as lub, the first heart sound, and dub, the second heart sound. The first heart sound is the closure of the valves between the top and bottom chambers of the heart, the atria and ventricles. The second heart sound is the closure of the valves controlling blood flow in and out of the heart.
A phonocardiogram is a special recording of heart sounds. This is a recording of a normal dog heart made with a digital stethoscope.
A heart murmur is an abnormally long heart sound. A murmur may be of no significance, an “innocent murmur,” or a murmur may be an indicator of disease. Murmurs are not exclusive to heart disease. Anemia and hyperthyroidism are two common causes of murmurs not resulting from heart disease. In dogs, heart murmurs occur when the valves between the heart chambers are leaky. In cats, heart murmurs occur because the heart muscle is abnormal and blood flow is turbulent.
Heart Murmur Grading Scale
Veterinary cardiologists use a scale from one to six to describe the intensity or loudness of heart murmur.
| Grade | Description |
| 1 | Almost inaudible murmur detected only with effort in a quiet room |
| 2 | Faint murmur requiring patience and experience to hear |
| 3 | Moderately loud and easily heard |
| 4 | Loud murmur, but not so loud it can be felt through the chest wall |
| 5 | Loud murmur that can be felt through the chest wall |
| 6 | Very loud murmur that can be felt through the chest wall and can still be heard if the stethoscope is lifted off the chest wall |
This system for describing heart murmurs helps communication between veterinarians. Veterinarians don’t use the scale to make medication decisions or determine the severity of the heart dysfunction. Echocardiograms and electrocardiograms are more helpful in determining treatment options and prognosis. Invariably, the loudness of a heart murmur increases over time. Don’t let that concern you – listen to the full story your pet’s cardiologist tells you about your pet’s heart condition.
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