Signs of a heart murmur in dogs
If you have been told your dog has a murmur, or you are watching for one because of their breed, the honest answer is that the murmur itself has no signs. What is worth watching is something else.
Medically reviewed by
Dr Laurent Locquet, DVM, PhD, Dipl. ECVIM-CA (Cardiology)
Veterinary cardiologist, Sonus Health Last reviewed September 03, 2026
A murmur is a sound, not a symptom
A murmur is a sound your vet hears through a stethoscope. It is not something your dog feels, and on its own it produces nothing you could notice at home. Most murmurs are found by chance, at an appointment booked for something else.
What can be noticed are the signs of a heart that is starting to work harder. Those come later, if they come at all, and many dogs with a murmur never develop them. They are worth knowing not to worry about daily, but so that you recognise them if they arrive.
What is worth watching at home
None of these mean heart disease on their own. Each has many ordinary explanations. They matter as a pattern, and as a change from what is normal for your dog.
Faster breathing at rest
A resting or sleeping breathing rate that has climbed and stayed up. This is the single most useful thing you can count at home.
Tiring sooner than usual
Slowing down on a familiar walk, lagging behind, or wanting to stop earlier than usual.
A cough that lingers
A cough that keeps coming back, especially at night or after lying down.
Fainting or collapse
Any wobble, collapse or faint. Uncommon, and always worth a call rather than a wait.
Going off food
Eating less than usual over a stretch of days, particularly alongside any of the above.
When to call your vet straight away
Some signs are not worth waiting on. Contact a vet the same day if your dog is struggling to breathe, breathing fast while resting or asleep, has pale, blue or grey gums, collapses or faints, or seems distressed and unable to settle.
Breeds where murmurs are more common
Some breeds are much more likely to develop a murmur, and to develop one earlier in life.
| Breed | Most common cause |
|---|---|
| Cavalier King Charles Spaniel | Mitral valve disease |
| Dachshund | Mitral valve disease |
| Chihuahua and small terriers | Mitral valve disease |
| Boxer | Aortic stenosis |
| Dobermann | Dilated cardiomyopathy |
Breed patterns follow published veterinary cardiology guidance. Individual dogs vary, and a breed on this list is not a diagnosis.
Listening between appointments
Hear what changes, between visits
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Common questions
Yes, and this is the usual case. Many dogs with a murmur behave completely normally for years. The absence of signs is genuinely reassuring about today, but it is not evidence that the murmur will stay unchanged, which is why vets ask to listen again.
To a vet through a stethoscope, a murmur is a whooshing or swishing sound between or across the normal heartbeats. You will not hear it by putting your ear to your dog's chest, and there is no reliable way to hear one unaided.
Almost always by listening with a stethoscope during an appointment booked for something else entirely, such as a vaccination or a limp. That is why a murmur so often arrives as a surprise.
Cavalier King Charles Spaniels are the most affected breed by a wide margin, followed by other small breeds such as Dachshunds, Chihuahuas and small terriers. Larger breeds such as Dobermanns and Boxers are prone to different heart conditions, some of which produce no murmur at all.
Most healthy dogs breathe between about 15 and 30 times a minute while asleep or fully at rest. Counting it now, while your dog is well, gives you their normal to compare against later. A resting rate that climbs and stays up is one of the more useful things an owner can spot at home.