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Understanding Heart Murmurs in Pets

A murmur is an abnormal heart sound that is heard between the normal heart beats. It is caused by turbulent blood flow across the valves of the heart. In most cases, this signifies that one of the valves that separates the chambers of the heart has an abnormality; either it is constricted, a condition referred to as stenosis, causing the blood to flow forward turbulently when the heart pumps, or it is weakened, a condition referred to as insufficiency, causing some blood to flow backwards when the heart pumps. 

Heart murmurs range in severity. They can be present in some puppies as they are growing, especially large and giant breeds, and resolve during the first few months of their life. Congenital heart conditions, those that are present at birth, will typically have murmurs associated with them, but the most common cause of heart murmurs in dogs is heart disease that develops with age, a condition referred to as acquired heart disease. 

Cats can be a little more complicated. Felines can actually develop a murmur just from being stressed or nervous at the veterinary clinic, a condition referred to as a “physiologic murmur.” This does not indicate any type of underlying heart disease, but a murmur could also be associated with heart disease in the cat. Another complicating factor is that some cats with underlying heart disease don’t even have a murmur. For this reason, further diagnostics are needed to determine the underlying cause of a heart murmur in a cat. 

Murmurs are typically graded on a 1 to 6 scale based on how loud they are. This also gives some indication on the severity and type of heart disease that might be present. Ultimately, further diagnostics, such as x-rays or an echocardiogram, are often needed to determine the cause of a heart murmur and the severity of the underlying condition. This is typically recommended with loud heart murmurs in dogs or long-standing murmurs that are becoming louder, although some murmurs never progress or cause any problems throughout the dog’s life. Recommendations are also based on dog breed and age. Since diagnosis can be a little trickier in cats, further diagnostics should be considered with any type of murmur. 

For more information on heart murmurs, please see:  Heart Murmurs in Dogs and Cats (from