Hope this helps, excerpt below. Click on link for full article.
https://www.mspca.org/angell_services/qa-with-angell-west-cardiologist-dr-rebecca-malakoff/
My dog/cat has a heart murmur. What does this mean?
A heart murmur is a “swooshing” sound heard while listening to the heart, instead of a crisp “lub-dub” sound. This typically indicates some turbulence to blood flow in the heart. It can be caused by a leaking valve, by an area of narrowing within the heart causing disturbance to blood flow, or by other abnormalities such as a defect or “hole” in a heart wall from birth. As in people, some pets can have a soft “innocent” murmur, where no significant heart disease is present. Murmurs are graded on a scale of 1 to 6 depending on how loud they are and how many places over the heart they are audible (with 6 being the loudest and most widespread). To determine the cause of a heart murmur, an echocardiogram, which is an ultrasound of the heart, is recommended.
