Murmur grading

Published on: 30th October 2019

A heart murmur is the term used to describe an abnormal heart sound that we hear whilst listening to the chest with a stethoscope. Heart murmurs are graded out of six with six being the loudest and one being the quietest.  A heart murmur is usually caused by turbulent blood flow which is often associated with leaking or narrowed heart valves or abnormal blood flow.

So is a grade six murmur always bad?

No – it all depends on the underlying cause. For example small holes in the heart can generate loud murmurs but rarely cause problems; however, if the problem is a narrowed heart valve, then the murmur loudness is proportional to the severity of the narrowing.

Are grade one murmurs safe?

No – once again it depends on the condition.  Especially in cats, severe heart disease can be present with only a quiet heart murmur so, once again, murmur loudness is only one of the criteria we use to assess patients.  We do sometimes encounter innocent murmurs in dogs and cats without any significant heart disease. Whilst innocent murmurs have certain characteristics, further tests are required to confirm the cause of a heart murmur.

Do all heart conditions have an audible heart murmur?

No – whilst most dogs with significant heart disease will have an audible heart murmur, cats don’t play by the rules so not all cats with heart disease will have a heart murmur.

Can murmur loudness vary?

Yes – some murmurs will vary depending on heart rate and also each individual vet will hear and perceive sound differently so there may be some variability in grading between individual vets. However this variability is reduced by experience and several years of post-graduate training culminating in accreditation as a RCVS Specialist in Cardiology – a qualification held by both Ruth and Sarah.

So how do we determine the cause and significance of a heart murmur?

Echocardiography (ultrasound of the heart) is a safe and painless way of assessing heart structure, size and function.  A detailed examination from both sides of the chest is required to fully examine all four cardiac chambers, valves and also the two large arteries leaving the heart.  At our practice echocardiography is performed without any sedation or anaesthesia – one of our nurses will gently hold your pet on a large padded bed whilst RCVS Specialists Sarah or Ruth perform the ultrasound scan.  We encourage you to stay during the echocardiographic examination to reassure your pet.

If you have any further questions then please get in touch.