What is a heart murmur?

A heart murmur refers to an noise made by the heart by the flow of blood through the valves. In some cases, this can be a normal finding, and in others, it can indicate a serious problem.


To understand what makes a murmur, it is important to understand the valves of the heart.

The heart relies on valves to separate each of the chambers from each other. There are four valves in the heart; the aortic valve, pulmonary valve, mitral valve, and tricuspid valve.

The heart can make several different types of noise, representing different components:

  • Heart sounds (“lub dub”)
    1. Usually, there are two heart sounds (called S1 and S2), one when both the aortic and pulmonary valve close, and one when the mitral and tricuspid valve close
    2. Extra heart sounds can be produced when the flow of blood is abnormal, either if the heart (specifically the left ventricle) is enlarged (S3), or if it is very stiff (S4).
  • Abnormal valves (“whooshing or swishing”)
    1. The heart valves can narrow down, called stenosis
    2. They can leak (let blood flow backwards), called regurgitation
  • Abnormal connections
    • if certain chambers have abnormal connections to each other, such as a shunt, then the blood passing through these connections can be heard as a murmur.
  • “Innocent” murmurs
    1. Some murmurs are present even though there is nothing structurally wrong with the heart; an example would be increased flow through the heart during pregnancy. It is very important that these murmurs are investigated and not assumed to be normal, as they may be mimicking something more serious.
  • Increased body requirements
    • As the body asks the heart to do more work, the increased flow of blood may also be heard. Examples include:
      • anaemia (low blood count)
      • hyperthyroidism (an overactive thyroid gland)

It is important to note that although the presence of these sounds may indicate a problem, and suggest severity, the most accurate way to confirm these findings is with an echocardiogram. Having no noise at all also doesn’t mean there is no problem; they are just a useful indicator when the doctor performs the examination.

When we listen to murmurs using a stethoscope, we are trying to hear the length, the frequency, and the quality of the murmur. A murmur that sounds flat for the entire noise can suggest a different problem to one that becomes loud and then becomes soft again.

Have a listen to the video below, which explains what the murmurs sound like and what they could mean.


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