Heart Murmur in Dogs: What It Means
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A heart murmur is an extra whooshing sound your vet hears when blood flows turbulently through the heart — it's a finding, not a diagnosis. Some murmurs are harmless (especially in puppies), while others signal heart disease such as a leaky valve. Murmurs are graded 1 to 6 by loudness, but grade alone doesn't tell the whole story; the real answer comes from further testing, usually an echocardiogram.
What a murmur actually is
A healthy heart makes two crisp sounds — the familiar "lub-dub." A murmur is an added noise caused by turbulent blood flow, often through a valve that isn't closing tightly or an opening that shouldn't be there. Your vet detects it with a stethoscope during a routine exam.
It's important to understand what a murmur is not: it isn't itself a disease or a guarantee your dog is sick. It's a clue that prompts your vet to ask why the blood flow is turbulent — and the answer ranges from completely benign to a heart condition that needs management.
How murmurs are graded
Vets grade murmurs by loudness on a scale of 1 to 6:
| Grade | What it means |
|---|---|
| 1–2 | Soft, hard to hear; often (not always) less serious. |
| 3–4 | Moderate to loud, easily heard; warrants investigation. |
| 5–6 | Very loud, with a vibration (thrill) you can feel through the chest wall. |
Practical take: loudness doesn't perfectly match severity. A soft murmur can accompany significant disease, and a loud one can be relatively benign — so the grade guides, but doesn't replace, further testing.
Common causes by life stage
Age is a big clue to what's behind a murmur:
- Puppies: many have an innocent (physiologic) murmur that's harmless and fades as they grow. Others have a congenital defect present from birth, such as a hole in the heart or a narrowed valve.
- Adult and senior small-breed dogs: the most common cause is degenerative (myxomatous) mitral valve disease — a gradually leaking valve, especially in breeds like Cavalier King Charles Spaniels, Chihuahuas and other small breeds.
- Large-breed dogs: murmurs can accompany dilated cardiomyopathy, where the heart muscle weakens.
- Any age: anemia, fever, pregnancy or infection (endocarditis) can also cause murmurs.
How your vet investigates it
Finding a murmur is the start of a conversation, not the end. Depending on your dog's age, breed and any symptoms, your vet may recommend:
- Echocardiogram (heart ultrasound) — the best test to see the heart's structure and function and pin down the cause.
- Chest X-rays — to check heart size and look for fluid in the lungs.
- Blood pressure, ECG, and blood tests including cardiac biomarkers like NT-proBNP.
These tests turn "there's a murmur" into a real diagnosis and stage, which is what determines whether your dog needs monitoring, medication, or nothing more than periodic checks.
Signs of heart trouble to watch at home
Many dogs with murmurs feel perfectly fine for years. But since heart disease can progress, learn the signs that mean it's time to call your vet:
- Coughing, especially at night or after lying down.
- Faster or labored breathing at rest — a resting breathing rate that's rising is an important early flag.
- Tiring easily, reluctance to exercise, or fainting.
- A swollen belly or weight/appetite loss.
Counting your dog's resting (sleeping) breathing rate at home is one of the most useful things you can do — a steady upward trend can flag developing heart failure before a crisis. Logging that number, along with cough or energy changes, gives your vet an early warning system and a real trend to review at each recheck.
Track your dog's heart between vet visits
Tavi lets you log your dog's resting breathing rate, coughing, energy and medications and chart them over time — so a rising trend that signals heart trouble surfaces early, and your vet gets real data instead of a snapshot. Free for your first pet.
Frequently asked questions
Is a heart murmur in a dog serious?
It depends entirely on the cause. Some murmurs, especially innocent puppy murmurs, are harmless, while others signal heart disease like a leaky valve. Because loudness alone doesn't reveal severity, your vet will usually recommend an echocardiogram to find out what's behind it.
Can a dog live a long life with a heart murmur?
Yes, many do. Plenty of dogs with murmurs never develop symptoms, and those with valve disease can often live comfortably for years with monitoring and, when needed, medication. Outlook depends on the underlying cause and how early it's managed.
What does the grade of a heart murmur mean?
Grades run from 1 (very soft) to 6 (very loud with a palpable vibration) and describe loudness, not severity. A soft murmur can accompany serious disease and a loud one can be relatively benign, so the grade guides testing rather than giving a diagnosis by itself.
Can a heart murmur in a dog go away?
Innocent puppy murmurs often disappear as the dog matures. Murmurs caused by structural heart disease generally don't go away and may progress, though some caused by fever, anemia or infection can resolve once the underlying problem is treated.
How do I know if my dog's heart murmur is getting worse?
Watch for coughing, faster or labored breathing at rest, tiring easily, fainting or a swollen belly. Tracking your dog's resting breathing rate at home is especially useful, since a steady rise can flag developing heart failure before other signs appear.
Tavi's guides are informational and not a substitute for professional veterinary advice, diagnosis or treatment. When in doubt, call your veterinarian. Sources: American College of Veterinary Internal Medicine (ACVIM) cardiology consensus; Merck Veterinary Manual; VCA Animal Hospitals; Cornell University College of Veterinary Medicine