Lub, Dub, and Something Else

By July 23, 2014 December 14th, 2018 Uncategorized

What is a heart murmur?

‘Heart murmur’ is the term used to describe any of the many abnormal sounds your veterinarian can hear when using a stethoscope on your pet.

Normally, the heart should make two distinct sounds, lub followed by dub. Any extra sound, most often a ‘whooshing’ occurring between the lub and the dub, will be considered a heart murmur!

The murmur itself is not dangerous, but the cause of the murmur could be. Not all heart murmurs are signs of serious problems, though. Many animals can live normal lives with heart murmurs and never receive any treatment at all. It can, though, be a sign of heart disease. This is why if a murmur is noticed, it is advised to work with your veterinarian to find out for sure if there is an underlying problem.

What causes heart murmurs?

What causes the murmur to exist is the blood flow in that area of the heart–or the kind of blood flow. In normal, healthy animals, the blood flow will be smooth and undisturbed–imagine a tranquil, babbling brook. When murmurs are present, this is due to the blood flow being turbulant–i.e. noisy and not smooth–imagine a surging river during a thunderstorm.

But what causes an animal’s blood flow to be turbulant in the first place? There are many reasons! The heart is a complex structure, involving valves, arteries, veins, and chambers to allow the blood to flow properly and in the right direction. If any of these elements experiences problems, then the whole system is thrown off–causing a murmur!

Most common causes of murmurs include:

  • Leaky mitral valves
  • Holes between chambers that should not be connected
  • Narrowing of a chamber or vessel
  • Thin blood (due to anemia for example)

How common are heart murmurs?

Heart murmurs are quite common, and receive one of six number grades which indicates the loudness of the murmur (1 being the softest, and 6 being the loudest). A loud murmur does not necessarily indicate severity! A murmur can be benign, meaning it has no apparent disease that explains the murmur, which is commonly seen in puppies and all ages of cats. Murmurs can even be heard if an animal gets too excited, and these are also considered benign. Animals can even be born with murmurs (these are called congenital murmurs)!

How is a heart murmur treated?

The murmur itself is not treated, but the underlying cause of the murmur can be treated depending on the severity of the heart problem, age of the patient, cost of treatment and other factors. A murmur can mean many things, so there is no way of knowing if it even needs treatment until your veterinarian performs a few tests.

For dogs, your veterinarian will likely be able to determine the severity of the murmur simply by listening. If warranted, a simple blood test can be performed that evaluates if the heart is under stress; this test is helpful to determine if the murmur is significant.

For cats, the severity and cause of the murmur is generally not determined by listening alone, and will often need further testing. This same blood test used for dogs to asses heart health is also available for cats.

In both cats and dogs, your veterinarian may elect to go one step further and perform x-rays, ultrasounds, or other imaging studies, even referring your pet to a specialist. It all depends on the pet!


Rishniw, M. (2007, January 29). Heart murmurs. Retrieved from Veterinary Partner website:

Content Contributor: Dr. Sandy Drury

LifeLearn Administrator

Author LifeLearn Administrator

H. Fraser is a LifeLearn author.

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