Heart Murmurs

A BASIC Guide to Heart Murmurs

So you’ve been to the vet, probably for a routine appointment and your vet says to you….“did you know he/she has a heart murmur”….at this point your mind goes into overdrive! First things first...don’t panic! Some murmurs are extremely hard to hear and unless the initial hearing of the murmur is a severe one it is worth giving it a few months (especially in young dogs) and going back for another listen (under vets advice of course), if the dog is excited or anxious (often an occurrence in the vets) rapid breathing sounds can mimic a murmur and can throw some vets that are unused to hearing minor murmurs.

A great tool we have in the UK are there are many breed health testing days around the country that have cardiac specialists performing heart tests for KC testing, (Boxers, CKCS etc) most of these will be happy to take bookings from any breed and it is worth it to get a specialist opinion at a sensible price and generally an automatic referral for any issues detected.

What is a heart murmur?

Quite simply a heart murmur is a disturbance in the blood flow through the heart, heard as an abnormal extra sound that occurs between or drowns out the normal heart sounds (lub, dub). Normally with a shooshing or whooshing sound. Heart murmurs have a grading scale from 1-6, 1 being the lowest and 6 being the highest and most severe;

  • Grade 1 - Barely audible
  • Grade 2 - Soft, but easily heard with a stethoscope
  • Grade 3 - Intermediate loudness
  • Grade 4 - Loud murmur that radiates widely, often including opposite sides of the chest
  • Grade 5 - Very loud, audible with stethoscope barely touching the chest, the vibration is also strong enough to be felt through the dogs chest wall
  • Grade 6 - Very loud, audible with stethoscope barely touching the chest, the vibration is also strong enough to be felt through the dogs chest wall

Be aware, the grading of a murmur is subjective as it is entirely based on the sound of the heart to the listener….this is another reason it is worth seeking a specialist cardiologist for a second opinion of a murmur.

Types of Murmur

Murmurs are generally split into 3 types;

  • Systolic - Murmurs that take place when the heart muscle contracts
  • Diastolic - Murmurs that take place when the heart muscle relaxes between beats
  • Continuous - Murmurs that happen throughout the regular heartbeat cycle

Most murmurs fall in the Systolic type and have a large range of causes which can include, Anaemia, Heartworm, Hyperthyroidism, Aortic valve insufficiency, Mitral valve issues.

Diastolic murmurs are rare in dogs and tends to be most associated with aortic insufficiency which is where the aortic valve does not close properly and leaks. Diastolic murmurs can also be caused by Mitral and tricuspid valve issues.

Continuous murmurs are most often caused by PDA (patent ductus arteriosus), which is a congenital heart defect and is a persistent opening between two valves within the heart.

Murmurs can also be called Innocent/Benign and Congenital & Acquired

  •  A benign or innocent murmur is usually a soft sound (grade 1-2) and there is no apparent cause. Whilst they can occur at any age they are often seen in puppies and can be intermittent, it is not uncommon for a n innocent or benign murmur to disappear by 12-16 weeks of age in a puppy.
  • A congenital murmur is present from birth and is associated with a defect within the heart that the dog was born with….these will sometimes not be picked up on until later in the dogs life.
  •  An Acquired murmur is what it says on the tin, a murmur acquire during the dogs life, they can also be Benign/Innocent but more often than not will be associated with a developing and/or degenerative heart or valve issue.

How is a murmur diagnosed?

Initially a murmur will be picked up by a stethoscope during a general check-up. Depending on the severity of the murmur it may then be worth further diagnostics. The first step would be to visit a specialist for a listen to give a more ‘practiced’ view of the murmur, they will then be able to advise what further diagnostics may be worthwhile...ECGs, ultrasounds etc to give a better view of the heart and its workings.

How do you treat a Heart Murmur?

Quite simply….you don’t, you can only treat the cause….in some cases this is simpler than others, hypothyroidism, heartworm, anaemia for example can be easily resolved...other more severe issues may not be treatable at all but with any sever murmur you should be under the care of a specialist who will give the best advice for any treatments and general lifestyle adjustments.

Heart murmur prognosis

Ok, so heart murmurs are scary and they can be serious however….most causes are treatable and in some cases (especially young puppies) they can resolve themselves. Equally it is not unusual for older dogs to develop a low grade heart murmur and live out a normal life. Every case is different but in most cases the dog will live a normal and happy life with little to no intervention.


The RCVS current list of Advanced Practitioners (Specialists) in Small Animal Cardiology for the UK can be found here - https://findavet.rcvs.org.uk/find-a-vet-surgeon/?filter-keyword=&filter-searchtype=surgeon&advanced16=true#primary-navigation

A number of these specialists will attend Breed Health Testing Days (it does not have to be a testing day for your breed) which is the perfect opportunity to get an initial specialist assessment, there is a Facebook group that these are normally advertised on - https://www.facebook.com/groups/170959846274011/

or the Kennel Club Journal is a valuable tool to locate Breed Health Testing - https://www.thekennelclub.org.uk/our-resources/publications/journal/

My story

I had a vet detect a heart murmur at 18 months old but say it wasn’t sounding serious and check in a few months, the vet I saw a few months later couldn’t hear one at all (although to be fair my young lady is a very anxious girl which does not help with a diagnosis). Shortly after I was looking to change insurance companies, the new insurance company I was looking at said if I could get a specialist to say there was no murmur they would cover her heart….off we went to a Boxer Club Open Show when she was just over 2 where Dr Dave Fisher was doing Heart Testing….we had a Grade 3 murmur diagnosed. Dave was great, got us an outpatient appointment booked at his surgery in Worcestershire where she had further scans and tests to give the full view. My girl has a grade 3 murmur on the left side with 2 leaks found, one of which is mitochondrial and a grade 2 on the right side…….which all sounds horrendous...but….she is incredibly fit and very healthy which helps her heart. She trains and competes at agility with no issues and Dave is more than happy for her to continue with this...it keeps her healthy. However, whilst she is great at the moment she will have annual check-ups with Dave to have a listen at her heart and currently biennial scans at his surgery to fully assess her hearts progress. She is under the careful watch of one of the RCVS specialists in Dave and will be for the rest of her life, there is no treatment for the issues her heart has, all we can do is wait and see how it goes at the moment.

Pam Sheppard











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