By Dial A Vet Veterinary Team
Hearing your vet say "I can hear a murmur" is unsettling, but a murmur is a sound, not a diagnosis. It is the noise of turbulent blood flow through the heart, and it can come from anything from a harmless puppy murmur to a leaking valve that will eventually need treatment. The most common cause in adult dogs is degenerative mitral valve disease, especially in small breeds such as Cavalier King Charles Spaniels. What matters is finding out why the murmur is there, how the heart is coping, and what to watch for at home.
Key takeaways
- A murmur is an abnormal heart sound caused by turbulent blood flow. Many dogs with murmurs have no symptoms for years.
- Murmurs are graded from 1 (very soft) to 6 (very loud). Loudness does not always match severity.
- Innocent murmurs are common in puppies and usually fade by around four to six months of age.
- An echocardiogram (heart ultrasound), often with chest X-rays, shows the cause and whether the heart is enlarged.
- Counting your dog's sleeping breathing rate at home is one of the best early warning tools for heart failure.
What causes heart murmurs
- Innocent (physiological) murmurs. Soft murmurs in young puppies with normal hearts. They should disappear as the puppy grows.
- Degenerative mitral valve disease. The mitral valve thickens and leaks with age. It is very common in small and medium breeds, including Cavaliers, Chihuahuas, Toy Poodles, Dachshunds, and Shih Tzus.
- Dilated cardiomyopathy (DCM). The heart muscle weakens and the chambers stretch. More common in large breeds such as Dobermanns, Great Danes, and Boxers.
- Congenital defects. Problems present from birth, such as patent ductus arteriosus, subaortic stenosis, or pulmonic stenosis. These are often found at puppy checks.
- Non-heart causes. Anaemia, fever, and some other conditions change blood flow and can create a murmur that goes away when the cause is treated.
Heartworm disease can also affect the heart. Read more about heartworm disease in dogs.
Signs that the heart is struggling
Many dogs with a murmur show no signs. When signs appear, they may include:
- A faster or more laboured breathing rate at rest or during sleep
- Coughing, especially at night or after activity
- Tiring more quickly on walks
- Restlessness at night or reluctance to lie down
- Fainting or collapse
- A swollen belly
- Pale, grey, or blue-tinged gums
These can point to congestive heart failure, where fluid builds up in or around the lungs or belly.
When to see a vet
Go to an emergency vet now if your dog:
- Is struggling to breathe, breathing with its mouth open at rest, or has blue, grey, or very pale gums
- Faints, collapses, or cannot settle because of breathing effort
- Has a sleeping breathing rate that stays well above its usual level and is rising
Book a same-day appointment if: your dog has a new cough, is tiring quickly, or its resting breathing rate has crept above 30 breaths per minute on more than one count.
Book a routine appointment if: a murmur was found at a check-up and your dog is well. Your vet will discuss whether and when further testing is worthwhile.
How vets assess a murmur
Your vet listens to where the murmur is loudest, its timing, and its grade. An echocardiogram is the key test, showing the valves, chamber sizes, and heart muscle function. Chest X-rays assess heart size and look for fluid in the lungs. Blood pressure, an ECG for heart rhythm, and blood tests (including a cardiac biomarker in some cases) may also be used.
For mitral valve disease, vets often use a staging system from the American College of Veterinary Internal Medicine. Dogs with a murmur but a normal-sized heart are usually monitored. Dogs whose heart has enlarged, but who do not yet have heart failure, may benefit from starting medication, which has been shown to delay the onset of heart failure in many dogs. Your vet or a veterinary cardiologist will guide this decision. Dogs with heart failure need ongoing treatment and regular rechecks.
Counting sleeping breathing rate
When your dog is deeply asleep in a cool room, count each rise of the chest for 30 seconds and double it. Most healthy dogs breathe fewer than 30 times a minute while asleep. Record it a few times a week so you know your dog's normal. A consistent rise is often the first sign of trouble, sometimes before any cough appears. There are free phone apps that make tracking easy.
Supporting a dog with a murmur
- Keep your dog lean. Extra weight makes the heart and lungs work harder.
- Keep exercise regular and moderate unless your vet advises otherwise.
- Avoid hard exercise in Australian summer heat.
- Keep up dental care, parasite prevention, and routine checks.
- If medication is prescribed, give it exactly as directed and never stop or change it without your vet.
FAQ
Can dogs live a normal life with a heart murmur?
Many do, often for years. Outlook depends on the cause and how the heart changes over time.
Does a louder murmur mean worse disease?
Not always. Loud murmurs often reflect significant valve leakage, but some serious heart diseases cause soft murmurs or none at all.
My puppy has a murmur. Should I worry?
Many puppy murmurs are innocent and fade. If it persists beyond about four to six months, or is loud, your vet will usually recommend an echocardiogram.
Can a dog with a murmur have an anaesthetic?
Often yes, with planning. Your vet may recommend heart tests first to tailor the anaesthetic.
Talk with a vet
If your dog has been diagnosed with a murmur and you want help understanding test results, breathing counts, or what to watch for, our vets can talk it through by video. Book a consult at dialavet.com. Breathing difficulty, collapse, or blue or grey gums are emergencies and need a hospital straight away.
References
- Merck Veterinary Manual. Heart Disease and Heart Failure in Dogs.
- American College of Veterinary Internal Medicine (ACVIM). Consensus guidelines on myxomatous mitral valve disease in dogs.
- Cornell University College of Veterinary Medicine. Cardiology patient information.
- VCA Animal Hospitals. Heart Murmurs in Dogs.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If your dog is struggling to breathe or collapses, contact a veterinary hospital immediately.