Heart Murmurs in Dogs
A heart murmur is an extra “whooshing” sound your veterinarian hears when blood flows turbulently through the heart. The most important thing to know: a murmur is a sign, not a disease in itself – and many dogs with a murmur live full, normal lives. What actually matters is the cause and how advanced it is, which your vet can find out.
Quick answer
A murmur grade tells you how loud the sound is, not how sick the heart is. The next step is to ask your vet what is causing the murmur and whether your dog needs staging with x-rays, an echocardiogram, blood pressure, an ECG, or a cardiology referral. Coughing, faster resting breathing, tiring easily, fainting, or collapse means the murmur needs prompt follow-up.
What is a heart murmur?
Normally a heartbeat sounds like a clean “lub-dub.” A murmur is an added sound caused by turbulent blood flow – often from a slightly leaky or narrowed valve. Some murmurs are completely harmless (“innocent” murmurs, common in puppies); others point to a heart condition that needs monitoring or treatment.
Heart murmur grades (1 to 6)
Vets grade murmurs by how loud they are, on a scale of I to VI:
| Grade | What it means |
|---|---|
| Grade I | Very soft – barely audible, only in a quiet room |
| Grade II | Soft, but easily heard with a stethoscope |
| Grade III | Moderate loudness |
| Grade IV | Loud, but no vibration felt on the chest |
| Grade V | Loud, with a “thrill” (vibration) you can feel on the chest wall |
| Grade VI | Very loud, with a thrill, audible even with the stethoscope lifted slightly off the chest |
Key point: the grade measures loudness, not how sick the heart is. A loud murmur is not always a failing heart, and a soft murmur can sometimes accompany serious disease. Grade is a clue – not a prognosis.
What causes a murmur in dogs?
- Mitral valve disease (MVD) – by far the most common cause in adult dogs, especially small breeds; a degenerating valve leaks. (You may see “mitral insufficiency” – it’s the same thing.)
- Innocent/physiologic murmurs – harmless, common in puppies, often fading by 4-6 months.
- Congenital defects – such as subaortic stenosis, PDA, or a hole in the heart (VSD).
- Other – dilated cardiomyopathy, anemia, fever, or heartworm disease.
Dog heart murmur life expectancy by grade
Grade 4 is the one owners ask about most, but the same rule applies across every grade: the grade alone does not answer it: the murmur grade itself does not set life expectancy. What matters is the underlying condition and its stage. A dog with a grade 4 murmur from early, well-managed mitral valve disease may live many years; the outlook changes only as the heart enlarges and approaches heart failure. That is why the next step after finding a murmur is to ask your vet how it should be staged. Depending on the dog, that may mean chest x-rays, an echocardiogram, blood pressure, an ECG, or referral to a cardiologist. See our guide to heart failure stages for what drives prognosis.
Life expectancy by murmur grade: what actually determines it
Because the grade measures loudness, the honest answer is the same at every grade: outlook is set by the underlying condition and its stage, not the number.
| Murmur grade | What the loudness tells you | What determines life expectancy |
|---|---|---|
| Grades 1-2 (soft) | Little on its own; a soft murmur can be incidental, but can also accompany serious disease | The underlying cause and its stage; ask your vet whether staging tests are needed |
| Grades 3-4 (moderate to loud) | Often mitral valve disease in smaller, older dogs; a dog with early, well-managed disease may live many years | How far the heart has enlarged and whether it approaches failure; chest x-rays or an echocardiogram stage it |
| Grades 5-6 (loud, with a thrill) | A louder murmur is not automatically a failing heart, but it usually prompts a full work-up | The staging findings, often with a cardiologist involved |
What to avoid if your dog has a heart murmur
- Don’t ignore it. Get it staged and keep recheck appointments – early treatment of MVD (at the right stage) can delay heart failure.
- Avoid extra weight. Obesity makes the heart work harder; keep your dog lean.
- Go easy on salty foods and treats if heart disease is present – excess sodium encourages fluid retention.
- Don’t over-exert a dog with advanced disease – but gentle, regular exercise is good and should not be stopped for a stable murmur.
Murmurs and coughing
A cough in a dog with a known murmur deserves a prompt vet visit. As mitral valve disease advances, the enlarging heart can press on the airway, and fluid can build in the lungs (heart failure) – both cause coughing. A new or worsening cough is one of the clearest signals the disease may be progressing.
Home monitoring: the resting breathing rate
The single most useful thing you can do at home is count your dog’s resting (or sleeping) breathing rate: the number of breaths in one minute while calm or asleep. Under about 30 breaths per minute is normal. A rate that climbs and stays above 30-40 can be an early sign of fluid on the lungs – call your vet.
When to see your veterinarian
Any newly found murmur should be evaluated. Seek care promptly for coughing, a rising resting breathing rate, tiring easily, fainting, or a swollen belly – and treat labored breathing or blue/pale gums as an emergency.
References and further reading
- American College of Veterinary Internal Medicine (ACVIM). 2019 consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of Veterinary Internal Medicine.
- VCA Animal Hospitals. Heart murmurs in dogs.
- Cornell University, Riney Canine Health Center. Canine heart health resources.
Frequently asked questions
Is a heart murmur in a dog serious?
It can range from completely harmless to a sign of significant heart disease. The murmur itself doesn’t tell you which – your vet stages it with imaging. Many dogs with murmurs live normal lives.
What is the life expectancy of a dog with a grade 4 heart murmur?
The grade alone doesn’t determine it. Life expectancy depends on the underlying disease (usually mitral valve disease) and its stage. Many dogs live years with proper monitoring and, when needed, medication.
Can a heart murmur in a dog go away?
Innocent puppy murmurs often disappear by a few months of age. Murmurs from valve disease usually don’t go away, but the disease can be managed for a long time.
Does a dog with a heart murmur need medication?
Not always. Early disease is often just monitored; medication (like pimobendan) is typically started at a specific stage of heart enlargement, on your vet’s recommendation.
What should I avoid if my dog has a heart murmur?
Weight gain, high-sodium foods, over-exertion in advanced disease, and skipping rechecks. Keep your dog lean, active in moderation, and on schedule with your vet.
Does my dog need an echocardiogram?
Often, if the murmur is more than a soft innocent one or your dog has symptoms. An echocardiogram is the best way to see the cause and stage. Your vet may start with a chest x-ray and decide from there, sometimes with a referral to a cardiologist.
Can my dog exercise with a heart murmur?
Most dogs with a stable murmur can and should keep up gentle, regular exercise. What to avoid is hard, exhausting exertion once disease is advanced. Your vet can tell you what is safe for your dog’s stage.
Is anesthesia safe for a dog with a murmur?
It can be, but it deserves extra care. Tell your vet about the murmur before any procedure so they can assess the heart first and tailor the anesthetic plan. Many dogs with murmurs are anesthetized safely with the right precautions.
How often should a heart murmur be rechecked?
It depends on the grade and cause. Stable, mild murmurs may be checked at routine visits, while murmurs from valve disease are watched more closely, sometimes every 6 to 12 months or sooner if signs change. Your vet sets the schedule.
This guide is educational and is not a substitute for veterinary diagnosis or care. If your dog has a heart murmur or any sign of heart trouble, talk to your veterinarian.
Is a stage 4 heart murmur the same as a grade 4?
People often mean grade 4 when they say stage 4, but the words are technically different. Murmurs are graded 1 to 6 by loudness. Heart disease is staged (A, B1, B2, C, D) by how far it has progressed. A "stage 4 heart murmur" almost always means a grade 4 murmur – and the stage of the underlying disease, found on an echocardiogram, matters far more for outlook than the murmur's loudness.
Is there a heart murmur life expectancy calculator for dogs?
No credible one exists, because the murmur grade alone cannot predict lifespan – outlook depends on the cause, the disease stage, and what an echocardiogram shows about the heart's size and function. The table above gives an honest way to think about risk by grade, and the echocardiogram is the closest thing to a real answer for your individual dog.
This guide is educational and is not a substitute for veterinary diagnosis or care. If your dog has signs of heart trouble, talk to your veterinarian.