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Heart Murmurs in Pets Explained


The heart is one of the body's most powerful organs. Thousands of times a day, it contracts to transport blood and supply oxygen and nutrients throughout the body. The heart rate of an adult dog is between 60 and 140 beats per minute, and a cat's between 140 and 180 beats per minute. There are two sounds that can be heard when listening to a regular heartbeat: a lub and a dub, anything else is refereed to as a murmur.


What is a heart murmur?

A heart murmur is an abnormal sound heard through a stethoscope when listening to your pet's heart. Normally, a veterinarian will hear two sounds, a “lub” and a “dub”, which are the sounds of the heart valves closing as blood circulates through the heart. An additional “whoosh” or “swish” noise are the sounds of turbulent blood flow within the heart, and is called a murmur.


What causes a heart murmur?

The short answer to this question is turbulent blood flow. Heart murmurs can be caused by:

  • Valve disease

  • Congenital or Hereditary Conditions

  • Dilated Cardiomyopathy

  • Heart disease


Turbulence can also be heard if your pet has anaemia, when the blood is too thin, or even if they are very excited, causing the heart to pump faster and harder than normal.

Do all murmurs sound the same?

No. Murmurs are graded by their intensity, from 1-6.

This grading system is simply a way for veterinarians to describe the loudness of a murmur. A veterinarian may use different names to explain the characteristics; this aids in communicating the murmur's features to other health care professionals, as certain forms of murmurs are more typically associated with various heart or valve problems.

Keep in mind that grading is subjective because it is dependent on the listener's perception of the sound. It's also difficult to identify if a pet has a murmur when it's enthusiastic or nervous as rapid breathing sounds can mimic a murmur. Click here to listen to some awesome murmur audio recordings. 


What is the Grading system?

  • Grade I – barely audible

  • Grade II – soft, but easily heard with a stethoscope

  • Grade III – intermediate loudness; most blood circulation murmurs are at least a grade III

  • Grade IV – loud murmur that radiates widely, typically heard on the opposite side of the chest

  • Grade V – very loud and audible with the stethoscope barely touching the chest; the vibration is strong enough to be heard through the dog’s chest wall

  • Grade VI – incredibly loud and can sometimes be heard without a stethoscope


What is a benign or “innocent” murmur?

Some murmurs are classified as benign (or innocent or physiological), implying that there is no obvious cause for the murmur. Often seen in puppies, these murmurs are not serious and generally disappear by 4 months of age. Murmurs associated with anaemia or excitement are also considered benign murmurs.


Diagnosing Dogs With Heart Murmurs

For pets with a high murmur grading, in order to determine exactly what is causing the murmur, your veterinarian may recommend a variety of tests, including blood tests, chest X-rays, ultrasound, and/or Electrocardiography.


Are there any treatments for Heart Murmurs?

Unless heart failure is evident, your pet will be treated as an outpatient. The course of treatment will be determined based on the associated clinical signs. Routine health checks (minimum of 6 monthly) and blood tests are recommended for all pets with murmurs.


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O’Halloran Hill Vet Centre

123 Main South Road
O’Halloran Hill, SA 5158

Hilton Vet Centre

142 Sir Donald Bradman Drive
Hilton, SA 5033