The vet says “your dog has a grade 4 heart murmur”.
What does that even mean? When I was first told Star had a grade 4 heart murmur, I remember thinking exactly this. Grade 4? How many grades are there? Grade 4 sounds bad.
It's overwhelming and scary. And to add to the confusion, the grading of heart murmurs and the staging of heart disease is 2 completely separate things.
So if you’ve been told your dog has a heart murmur, this guide is here to explain it a little more simply.
What is a heart murmur?
A heart murmur is an unusual sound a vet can hear when listening to the heart with a stethoscope.
Instead of the normal “lub-dub” heartbeat, blood flow creates an extra sound caused by turbulence within the heart. But a murmur itself is not a diagnosis; it’s a sign that something may be happening within the heart.
Some murmurs are harmless, while others are linked to heart disease.
What do the grades mean?
Heart murmurs are usually graded from 1 to 6 depending on how loud they sound.
Grade 1
Very quiet and difficult to hear.
These murmurs may not always indicate significant disease.
Grade 2
Soft but easier for a vet to hear.
Still relatively mild, but your vet may recommend monitoring over time.
Grade 3
Moderately loud.
At this stage, vets often recommend further investigations, especially if symptoms are present.
Grade 4
Loud murmur that can usually be heard clearly on both sides of the chest.
This often suggests more significant changes within the heart.
Grade 5
Very loud with a “thrill” — a vibration that can sometimes be felt through the chest wall.
Grade 6
The loudest grade possible.
These murmurs can often be heard even with the stethoscope only lightly touching the chest.
Does a higher grade always mean worse disease?
Not always.
One thing I learned through Star’s journey is that murmur grades don’t always tell the full story. Some dogs with lower grade murmurs can still have significant heart disease, while others with louder murmurs may remain stable for long periods of time.
The grade is simply one piece of the puzzle.
Final thoughts
A heart murmur diagnosis can feel frightening at first, but many dogs continue to live happy, joyful lives for years with proper monitoring and care.