Home Heart Murmur in Dogs

Heart Murmur in Dogs: Grades, Causes and What to Do

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • A murmur is an extra sound from turbulent blood flow. It's a clue, not a diagnosis.
  • Murmurs are graded 1 (very soft) to 6 (very loud). Louder murmurs are more likely to mean significant disease.
  • Soft murmurs are common in young puppies and usually fade by about 4 to 5 months.
  • In small older dogs, a new murmur usually means mitral valve disease.
  • X-rays and an echocardiogram show whether the heart is enlarged and whether treatment should start.
  • Many dogs live normal lives with a murmur; watch for coughing, tiring easily and fast breathing at rest.

Table of Contents

Research What it is Grades Puppies Causes Tests Treatment Life expectancy Daily life FAQ Sources

Heart and Blood QuickLinks

Heart Disease Congestive Heart Failure Heart Murmurs Heart Rate High Blood Pressure Heartworm Overview of Dog Blood Blood Disorders

A heart murmur is an extra "whooshing" sound your vet hears through a stethoscope, caused by turbulent blood flow in or near the heart.1 A murmur is a clue, not a diagnosis. Soft murmurs in young puppies are often harmless, while a new murmur in an older small dog usually means mitral valve disease.1,2 Many dogs with a murmur live normal lives for years, but some murmurs signal heart disease that needs testing and treatment.1,3 This guide explains murmur grades, puppy murmurs, causes, tests, treatment and life expectancy.

See a vet promptly if your dog has a murmur and:

  • Breathes fast or hard while resting or asleep (consistently over 30 breaths a minute when asleep)4,5
  • Coughs, especially at night or when lying down6
  • Tires easily, faints or collapses6
  • Has blue, gray or very pale gums, or a swollen belly; these are emergencies7,6
Labeled diagram of a dog's heart showing the chambers and the mitral, tricuspid, aortic and pulmonary valves
Most murmurs in older dogs come from a leaky mitral valve, between the left atrium and left ventricle.

What the Research Shows

  • Puppy murmurs are common. Up to 20% of healthy 7-week-old puppies have an innocent murmur, usually soft (grade 1 or 2 out of 6).8
  • Murmurs are common in small breeds. In UK vet practices, a heart murmur was the single most common disorder recorded in Cavalier King Charles Spaniels, found in about 31% of them.9
  • A murmur doesn't mean heart failure is coming. Only about 30% of dogs with a leaky mitral valve ever develop congestive heart failure.3
  • Testing changes treatment. When a murmur comes with enough heart enlargement, starting pimobendan delayed heart failure or cardiac death by about 15 months (median) in the EPIC trial of 360 dogs.10,2

What Is a Heart Murmur in Dogs?

Normally, blood flows smoothly through the heart and you hear only the "lub-dub" of the valves closing. A murmur happens when blood flow becomes turbulent, for example when it leaks backward through a valve that doesn't close properly, squeezes through a narrowed valve, or flows through an abnormal opening.1,11 Some murmurs come from problems outside the heart, such as anemia, fever, low blood protein or pregnancy; these may go away once the cause is treated.1

Heart Murmur Grades in Dogs

Vets grade murmurs from 1 to 6 by how loud they are:12,1

  • Grade 1: very quiet and hard to hear, in one spot.
  • Grade 2: quiet but easy to hear.
  • Grade 3: about as loud as the normal heart sounds, often heard in more than one spot.
  • Grade 4: louder than the normal heart sounds.
  • Grade 5: louder than the heart sounds, with a vibration ("thrill") that can be felt through the chest wall.
  • Grade 6: very loud, with a thrill, and can be heard with the stethoscope just off the chest.

In mitral valve disease, louder murmurs (grade 3 or more) are more likely to come with an enlarged heart, but loudness alone doesn't tell your vet how severe the disease is; that takes X-rays or an echocardiogram.2

Heart Murmurs in Puppies

Innocent (physiologic) murmurs are common in growing puppies. They usually appear at 6 to 8 weeks, are soft (grade 1 to 2), cause no signs, and are typically outgrown by about 4 to 5 months of age.1,8 Your vet will usually recheck the puppy in a few weeks.1

A murmur that is loud, has a thrill, is heard in diastole, is continuous, or is still present at about 6 months of age suggests a congenital heart defect, and the puppy should see a cardiologist.8,11 A puppy with a murmur that is small for its age, tires quickly or breathes fast needs a prompt exam rather than a recheck in a few weeks.8 Several defects, such as patent ductus arteriosus (PDA) and pulmonic stenosis, can be corrected if they're found early.8,11,13

Causes of Heart Murmurs in Adult Dogs

  • Mitral valve disease: by far the most common cause in older small and medium breeds. Murmurs can appear as early as 4 to 6 years of age, and Cavaliers often develop them younger: about half have a murmur by age 5.14,2,15
  • Dilated cardiomyopathy: in large breeds, often with a soft murmur or an irregular rhythm.16,1
  • Congenital defects such as subaortic stenosis, pulmonic stenosis and PDA.11
  • Bacterial endocarditis, an infection of a heart valve.1
  • Non-heart causes: anemia, fever, low blood protein, pregnancy, obesity or being very thin.1

Cavaliers, Chihuahuas, Poodles, Shih Tzus, Yorkshire Terriers and Whippets are at higher risk of mitral valve disease.17 See heart disease in dogs.

Tests for a Dog With a Heart Murmur

  • Echocardiogram (heart ultrasound): the best test to find the cause of a murmur and measure the heart.2,1
  • Chest X-rays: show heart size and fluid in the lungs; recommended for dogs being evaluated for valve disease.2
  • NT-proBNP blood test: helps decide whether a cough or breathing problem is likely due to the heart.2
  • ECG, if the rhythm is irregular, and blood tests for anemia and other non-heart causes.1

Testing matters because it decides whether treatment should start now or the murmur can simply be watched.2 Before anesthesia (for example, a dental cleaning), tell your vet about the murmur; dogs with heart disease may need tests, or a few weeks of heart treatment, before anesthesia.18

Treatment of Heart Murmurs in Dogs

The murmur itself isn't treated; the cause is.1

  • Innocent puppy murmur: no treatment; recheck as advised.1
  • Mitral valve disease without heart enlargement (Stage B1): no medication; recheck every 6 to 12 months.2
  • Mitral valve disease with heart enlargement (Stage B2): pimobendan is recommended to delay heart failure.2,10
  • Heart failure: several medications, including a diuretic. See congestive heart failure in dogs.
  • Congenital defects: some can be closed or opened by surgery or catheter procedures.11,13
  • Non-heart causes: treat the anemia, fever or other problem.1

There are no proven "natural" treatments for a murmur, and supplements shouldn't replace prescribed medicine.2 See dog heart medicine.

Life Expectancy for Dogs With a Heart Murmur

It depends entirely on the cause. Innocent and treatable non-heart murmurs have an excellent outlook, and many corrected congenital defects do very well.1 Most dogs with early mitral valve disease live for years, and only about 30% ever develop heart failure.3,2 A grade 4 or louder murmur from valve disease is more likely to come with heart enlargement, so testing and treatment matter more.2 Once heart failure develops, life expectancy is usually months to a year or two.19,20 Murmurs from DCM carry a poorer outlook if heart failure develops.1,16

Daily Life With a Heart Murmur

  • Count sleeping breaths: a few times a week, count your dog's breaths for 30 seconds while asleep and double it. Healthy dogs average about 13; call your vet if it's consistently above 30, and go now if it's above 30 with labored breathing.21,5,4
  • Walks: normal walks are usually fine for dogs without heart failure. Once heart failure develops, keep walks short and gentle.22
  • Food: keep your dog lean and avoid very salty treats and table scraps; stricter sodium limits are for dogs with heart failure.23,6
  • Checkups: keep up with rechecks, since murmurs can get louder as disease progresses.2

Frequently Asked Questions

Should I worry if my dog has a heart murmur?

Not necessarily. Many murmurs are mild or harmless. But a new murmur in an adult dog should be checked with X-rays or an echocardiogram to find the cause and decide whether treatment is needed.

How long can a dog live with a heart murmur?

Many dogs live normal lifespans. It depends on the cause: innocent murmurs don't shorten life, and most dogs with early valve disease live for years. Life expectancy drops once heart failure develops.

Is a grade 4 heart murmur in a dog serious?

It's more likely to mean significant heart disease than a soft murmur, so your vet will usually recommend an echocardiogram or X-rays. Many dogs with grade 4 murmurs are treated and do well for a long time.

Is it common for puppies to have heart murmurs?

Yes. Up to 1 in 5 puppies at about 7 weeks has a soft, innocent murmur, which usually disappears by about 4 to 5 months. Loud or persistent murmurs need a cardiology check.

Are dogs in pain with a heart murmur?

No. A murmur is just a sound and isn't painful. Signs of heart failure, such as breathlessness and coughing, are what to watch for.

Can I walk my dog with a heart murmur?

Usually yes. Normal exercise is fine for most dogs without heart failure. If your dog has heart failure, keep walks short and stop if they breathe hard or lag behind.

What should I not feed a dog with a heart murmur?

Avoid very salty foods such as deli meats, cheese and chips, and limit treats. Dogs in heart failure may need a lower-sodium diet chosen with your vet.

Can a heart murmur go away on its own?

Innocent puppy murmurs and murmurs from anemia or fever often do. Murmurs from valve disease or congenital defects don't go away without treatment of the cause.

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Sources and further reading

This article was rewritten and fact-checked on October 15, 2026 against current veterinary references and specialist guidelines:

  1. Hyland K, Weir M, Yuill C, Panning A. Heart murmurs in dogs. VCA Animal Hospitals, October 2026.
  2. Keene BW, Atkins CE, Bonagura JD, et al. ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of Veterinary Internal Medicine, 2019. Also in the IVIS ACVIM consensus statements collection.
  3. Kittleson MD. Myxomatous atrioventricular valve degeneration in dogs and cats. Merck Veterinary Manual, May 2025.
  4. Porciello F, Rishniw M, Ljungvall I, et al. Sleeping and resting respiratory rates in dogs and cats with medically-controlled left-sided congestive heart failure. The Veterinary Journal, 2016.
  5. Cummings School of Veterinary Medicine at Tufts University. Monitoring heart disease treatment at home. HeartSmart.
  6. Kittleson MD. Heart failure in dogs. Merck Veterinary Manual (pet owner version), updated September 2024.
  7. Cunningham SM, Roderick KV. Heart disease in dogs. Merck Veterinary Manual (pet owner version), updated September 2024.
  8. Szatmári V. How can we differentiate innocent murmurs from pathologic ones in asymptomatic puppies? European Veterinary Conference Voorjaarsdagen, 2018. Conference proceedings hosted by IVIS.
  9. Summers JF, O'Neill DG, Church DB, Thomson PC, McGreevy PD, Brodbelt DC. Prevalence of disorders recorded in Cavalier King Charles Spaniels attending primary-care veterinary practices in England. Canine Genetics and Epidemiology, 2015.
  10. Boswood A, Häggström J, Gordon SG, et al. Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: the EPIC study, a randomized clinical trial. Journal of Veterinary Internal Medicine, 2016.
  11. Tou SP. Congenital and inherited disorders of the cardiovascular system in dogs. Merck Veterinary Manual (pet owner version), updated September 2024.
  12. Identifying heart murmurs and other heart sounds. Veterinary Practice.
  13. Monnet E, et al. Heart and great vessels. In: Bojrab MJ, ed. Current Techniques in Small Animal Surgery, 5th ed. Hosted by IVIS.
  14. Weir M, Llera R, Ward E. Mitral valve disease in dogs. VCA Animal Hospitals, March 2023.
  15. Universities Federation for Animal Welfare. Cavalier King Charles Spaniel: mitral valve disease. Genetic Welfare Problems of Companion Animals.
  16. Kittleson MD. Dilated cardiomyopathy in dogs and cats. Merck Veterinary Manual, September 2024.
  17. Mattin MJ, Boswood A, Church DB, et al. Prevalence of and risk factors for degenerative mitral valve disease in dogs attending primary-care veterinary practices in England. Journal of Veterinary Internal Medicine, 2015.
  18. Grubb T, Sager J, Gaynor JS, et al. 2020 AAHA anesthesia and monitoring guidelines for dogs and cats. Journal of the American Animal Hospital Association, 2020.
  19. Maharaj N. Congestive heart failure in dogs: what you need to know. American Kennel Club, August 2026.
  20. Häggström J, Boswood A, O'Grady M, et al. Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: the QUEST study. Journal of Veterinary Internal Medicine, 2008.
  21. Rishniw M, Ljungvall I, Porciello F, Häggström J, Ohad DG. Sleeping respiratory rates in apparently healthy adult dogs. Research in Veterinary Science, 2012.
  22. Cummings School of Veterinary Medicine at Tufts University. Reduced ability to exercise. HeartSmart.
  23. Cummings School of Veterinary Medicine at Tufts University. Heart disease: nutrition. HeartSmart.

About this article

Last updated : fully rewritten using the ACVIM consensus guidelines, VCA, the Merck Veterinary Manual, IVIS-hosted conference proceedings and published studies; added the murmur grading scale, innocent puppy murmurs, causes, tests, treatment, life expectancy, daily life with a murmur, a key takeaways summary and FAQ.

This page is for general information and is not a substitute for an exam by your veterinarian.