Heart murmurs in Dogs and Cats: Everything you need to know

A complete pet owner guide to signs, causes, diagnosis, stages, treatment, home care and prognosis

Written by:
Rita Ng
Posted on: August 13, 2026

Key symptoms	Often no visible signs; can progress to rapid breathing, reduced exercise tolerance, coughing, fainting or pale/blue gums
Commonality	Can occur in both dogs and cats; more often associated with underlying heart disease in dogs
Transmission	Not contagious
Impact on health	Varies from harmless innocent murmurs to signs of serious underlying heart disease; the murmur itself is not a disease
Treatment cost	Varies depending on the underlying cause and tests required; some pets may only need monitoring, while others require lifelong medication
Treatment duration	Depends on the cause; some murmurs require no treatment, while underlying heart disease may need lifelong management
Ease of prevention	Often difficult to prevent, especially when caused by inherited or age-related heart disease; regular veterinary check-ups can help with early detection

Most affected dog breeds

Most affected cat breeds

What you should know

A heart murmur is a sound, not a diagnosis. It can be innocent or associated with an underlying disease.
The loudness of a murmur does not always indicate the severity of heart disease.
A murmur found incidentally during a routine exam doesn’t necessarily mean your pet is sick or in danger right now
Further investigation may be recommended to determine whether the murmur is associated with heart disease or another condition.

What you can do

Keep up with regular veterinary examinations so that new or changing murmurs can be detected early.
Tell your veterinarian about any new symptoms you have noticed at home, even if they seem minor.
Feed a balanced diet that helps your pet maintain a healthy body weight, to reduce unnecessary strain on the heart
Don’t panic if a murmur is found, but don’t ignore it either. Timely investigation can give your pet the best chance of early management if an underlying problem is present.

When the vet mentioned a heart murmur, should we be immediately concerned? Before you panic, a heart murmur is not a diagnosis; it is a sound. Some murmurs are harmless, while others can be associated with heart disease or another underlying condition. Here is everything you should know about heart murmurs.

What Is a heart murmur in a dog or cat?

A heart murmur is an abnormal turbulent heart sound that occurs when blood flow is disrupted rather than flowing smoothly through the heart. Normally, a heartbeat produces two crisp sounds, ‘lub-dub’. When a heart murmur is present, a vet can hear a whooshing sound through a stethoscope during examination.

Imagine a river flowing through a dam with gates that control the water. When water moves through a wide, smooth channel, it flows quietly. But if the river is narrow or there is a leaky gate which makes the water flow backwards, it creates a turbulent noise. This explains why a heart murmur may happen ¹.

How are murmurs graded?

If a heart murmur is detected, your vet will grade the heart murmur from I to VI, based on how loud it is and how it can be detected. However, it does not always indicate the severity of heart disease ¹.

Grade	Description
Grade I	Very soft; requires a quiet room and careful listening
Grade II	Soft but readily heard in one region
Grade III	Moderately loud without a palpable vibration
Grade IV	Loud, usually heard over a wider area
Grade V	Very loud with a palpable chest-wall thrill
Grade VI	Very loud, with a thrill, and audible with the stethoscope slightly off the chest

Is a grade VI murmur always more dangerous than a grade II?

Not necessarily.

The grade does not always correlate with the severity of the disease. A loud murmur doesn’t automatically mean that there is advanced heart disease, and a quiet murmur doesn’t mean that everything’s fine. Particularly in cats, murmur intensity has a poor correlation with actual disease severity and does not reliably predict the presence or severity of structural heart disease ².

What are the types of heart murmur?

Heart murmurs can broadly be classified as innocent or functional murmurs and pathological murmurs.

An innocent murmur is a type of murmur that occurs even when the heart structure is normal, but due to the blood flow, there is a soft sound.

Causes of innocent murmur:

Rapid heart rate
Anaemia
Fever
Immature cardiac anatomy of a young animal

On the other hand, pathological murmurs are caused by an actual structural or functional problem: a leaky valve, a hole between chambers, thickened heart walls, or a narrowed vessel.

Heart murmurs can broadly be classified as innocent or functional murmurs and pathological murmurs.

What causes heart murmurs in pets?

The causes of heart murmurs can vary depending on the pet’s age, species and underlying health.

Puppies and Kittens

Congenital heart defects: some puppies and kittens are born with heart problems that affect how blood flows through the heart. Certain breeds are more prone to specific conditions ¹.

Patent ductus arteriosus (PDA): A blood vessel that should close shortly after birth remains open, causing abnormal blood flow.
- Commonly affected breeds: Australian Shepherd, Belgian Shepherd, Cavalier King Charles Spaniel, Chihuahua, Cocker Spaniel, Collie, Doberman Pinscher, English Springer Spaniel, German Shepherd, Keeshond, Kerry Blue Terrier, Labrador Retriever, Maltese, Newfoundland, Pomeranian, Poodle (Toy and Miniature), Shetland Sheepdog and Welsh Corgi.

Pulmonic stenosis: The valve that controls blood flow from the heart to the lungs is narrowed, making the heart work harder.
- Commonly affected breeds: Airedale Terrier, American Staffordshire Terrier, Basset Hound, Beagle, Boxer, Boykin Spaniel and Chihuahua.

Innocent murmurs: Soft murmurs can occur in growing puppies and kittens due to rapid blood flow during development. These are usually harmless and often disappear by six months of age.

Are all heart murmurs in growing pets a concern?

Not always. In growing puppies and, less commonly, in kittens, innocent murmurs can develop because their cardiovascular systems are still developing. In most cases, it resolves by six months. However, a recheck at six months is recommended to make sure the sound has actually disappeared ³.

Adult dogs and cats

There are many causes of heart murmurs in adult dogs and cats. We will discuss the most common diseases in dogs and cats below.

What is the most common cause of heart murmurs in adult dogs?

Myxomatous Mitral Valve Disease (MMVD) is the most common cause of heart murmur in adult and senior dogs, especially smaller breed dogs.

Normally, the mitral valve, which separates the left atrium (upper chamber) and left ventricle (lower chamber), works like a one-way flap door. Blood comes in through the door, which then closes tightly so the blood can’t flow back the wrong way.

In MMVD dogs, the valve’s flaps get thickened and floppy, like an old rubber door hinge that doesn’t seal properly so ‘the door’ doesn’t close all the way. This causes some blood to leak backwards every time the heart beats, creating the murmur.

At-risk dog breeds: ⁴

What is the most common cause of heart murmurs in cats?

Hypertrophic Cardiomyopathy is the most common cause of heart murmurs in cats. In cats with this condition, the heart muscle (the wall of the heart) thickens.

The thicker heart muscle can become stiff, which makes it harder for the heart to relax, and the heart may not fill as efficiently. This can change the way blood moves through the heart and may produce a murmur.

At-risk cat breeds ¹:

Are heart murmurs more common in dogs or cats?

Heart murmurs can occur in both dogs and cats. They are more commonly associated with underlying heart disease in dogs, while heart murmurs in cats can be more unpredictable and may occur even when the heart is structurally normal. Innocent murmurs are also more commonly seen in puppies than kittens and often disappear as puppies grow.

A heart murmur in a cat is less predictable than in a dog. In one study done by Payne (2015), 70% of healthy cats with a heart murmur were found to have no underlying structural heart disease when further assessed with echocardiography. These are known as innocent murmurs. This demonstrates why a heart murmur in a cat should not automatically be assumed to be either harmless or a sign of serious disease ⁵.

Why can heart murmurs in cats be difficult to interpret?

One contributing factor is dynamic obstruction, where blood flow is temporarily disrupted by changes in heart rate or muscle contraction rather than a fixed structural problem. Heart murmurs in cats also vary with stress. When the cat calms down, the murmur may disappear.

Cats are also naturally good at hiding signs of illness, which makes symptoms harder to detect. With all these varying factors, it can be hard to detect if the murmur in a cat is truly pathological by stethoscope, so further diagnostics are needed.

Does a heart murmur always mean it's because of the heart?

Not always. A murmur is just the sound of turbulent blood flow, and several conditions outside the heart itself can create that turbulence without any structural heart disease being present: ⁶

Anaemia: thinner blood flows more turbulently, especially at higher velocity
Hyperthyroidism (particularly in older cats): a hormonal disease that drives up heart rate and blood flow force
Fever: increases heart rate and cardiac output, which can produce turbulent flow
Pregnancy: increased blood volume and cardiac output can cause a temporary murmur

What signs should I watch for at home?

A heart murmur can be difficult to pick up if you don’t have a stethoscope. However, some pets with underlying heart disease may develop noticeable changes at home ⁷

Watch for:

Rapid breathing, at rest or during sleep
Reduced exercise tolerance, reluctance to play, or unusual fatigue on walks
Coughing
Fainting
Pale or bluish gums
Sudden hind-limb weakness or pain in cats

Seek urgent veterinary care if your pet has severe or laboured breathing, open-mouth breathing, blue or grey gums, collapses, or is otherwise in obvious respiratory distress. ¹

How do vets diagnose a heart murmur?

Auscultation, or listening to the heart with a stethoscope, is usually the first step in detecting a murmur. Depending on the findings, further diagnostic tests may be recommended ¹ ⁸

Test	What is tests	Typical use
Auscultation	Whether a murmur is present, its grade, and location	Initial detection, routine screening
Echocardiogram	Valve structure, chamber size, blood flow direction	Confirming diagnosis, staging disease
Chest X-ray	Heart size, heart shape, lung fluid	Assessing heart enlargment and possible congestive heart failure
ECG	Heart rhythm and electrical activity	Detecting arrhythmias (irregular or abnormal heartbeat) besides a murmur
Blood pressure test	Any systemic high blood pressure that	Ruling out hypertension as a cause or complication
NT-proBNP / Troponin-I blood test	Cardiac stress and muscle damage markers. If the result is high, then	Useful in screening cats with murmurs

What is the most useful test for finding the cause of a murmur?

An echocardiogram (heart ultrasound) provides detailed information about the heart’s structure, valves, chamber size and blood flow. It is particularly useful when your veterinarian needs to determine whether a murmur is associated with structural heart disease, assess its severity, and guide the most appropriate treatment.

Other tests, such as chest X-rays, ECG, blood pressure measurement and blood tests, may be recommended depending on the individual pet and suspected cause. ¹ ⁹

How are heart murmurs treated and managed?

Your veterinarian may recommend treatment for the underlying condition causing the heart murmur. Depending on the diagnosis, this may include medication, supportive care, surgery, or a combination of these ¹⁰.

If the murmur is caused by a non-cardiac issue like anaemia, fever, or hyperthyroidism, treating that underlying condition often resolves the murmur entirely.

If it’s caused by a structural heart problem, such as a leaky or narrowed valve, treatment usually focuses on managing the condition and slowing its progression. This can be done through medications that support heart function, reduce fluid buildup, or ease the heart’s workload, rather than “curing” the murmur itself.

In some cases, especially if the murmur is innocent and not linked to any disease, no treatment is needed at all but just regular monitoring.

How can you monitor your pet at home?

For pets with known or suspected heart disease, counting your pet’s breathing rate at home can be a useful way to monitor for signs of heart condition deterioration.

Protocol:

Wait until the pet is fully asleep or quietly resting. Do not count immediately after exercise, during panting, or while a cat is purring.
Watch the chest or flank. One rise and fall equals one breath.
Count for 30 seconds and multiply by two, or count for a full minute.
Record the rate, date, time, medication changes, appetite, cough, and breathing effort. Build a baseline when the pet is stable.
If a comfortable pet has one unusual reading, repeat it later under ideal conditions. Contact your vet if there is a consistently higher reading than normal.
Do not wait for another count if breathing is laboured, the mouth is open, the gums look blue or grey, or the pet collapses. Those signs warrant emergency care.

To minimise stress on the heart when there’s a structural heart problem, feeding a balanced diet that helps your pet maintain a healthy body weight can

Beyond diet, a few habits go a long way in supporting long-term heart health:

Year-round parasite prevention (where heartworm is endemic)
Routine examinations
Prompt investigation of new signs all help improve early detection and reduce preventable contributing factors.

What Is the life expectancy for a pet with a heart murmur?

There is no single answer because life expectancy depends on the underlying cause of the murmur ¹

Pets with an innocent murmur typically have a completely normal life expectancy, since there’s no actual disease affecting the heart.

For pathological murmurs caused by structural heart disease, life expectancy varies widely depending on the specific condition, how early it’s caught, and how well it responds to treatment. Some pets live for years with proper management, while more advanced or severe cases can significantly shorten lifespan.

For example, mitral valve disease is a progressive condition that is usually managed with lifelong medication to help maintain a good quality of life. Although medication can slow disease progression and relieve symptoms, it cannot cure the disease.

Should you worry if your vet detects a murmur at a routine check-up?

Concerned, yes. Panicked, no.

A murmur found incidentally, meaning your pet showed no symptoms and this was just picked up during a standard physical examination, is common and doesn’t automatically mean disease.

The goal is to understand why the murmur is present, rather than judging your pet’s health based on the sound alone.

Can a heart murmur disappear on its own?

Yes, but only in some conditions.

Innocent murmurs in puppies usually disappear by 6 months as the heart finishes developing.

Murmurs caused by non-heart-related problems like anaemia or fever often disappear once the underlying problem is treated.

Feline dynamic murmurs caused by stress can resolve the moment a cat relaxes, only to return at the next stressful vet visit.

However, a murmur that is caused by a structural defect or degenerative valve disease would require ongoing management rather than waiting it out. ¹

Heart murmurs in cats and dogs:
key takeaways

A heart murmur isn’t necessarily a bad thing. If your pet has a heart murmur, it simply means further investigation is needed.

Some pets can live a completely normal life with a soft murmur, while others may need a long-term treatment plan depending on what the diagnosis reveals.

Heart murmurs in Cats and Dogs: Frequently Asked Questions

Can a heart murmur be cured?

Rarely. Some congenital defects can be surgically corrected. Many acquired heart conditions, however, are managed long-term rather than cured.

Does every dog breed get the same murmurs?

No. Predisposition varies significantly by breed, with small breeds leaning toward mitral valve disease and certain large breeds more prone to congenital defects like subaortic stenosis.

Should I get a second opinion if my vet hears a new murmur?

If your regular clinic doesn’t have access to echocardiography, a referral to a veterinary cardiologist is entirely reasonable and often recommended.

Can pet insurance cover a heart murmur?

Petsy pet insurance does cover conditions of heart murmur when the heart murmur is detected after the policy has commenced. If the heart murmur was identified by a veterinarian before the insurance policy started or during the 14-day waiting period, it would be considered a pre-existing condition and would not be covered under the policy. Always check the specific policy terms and conditions.

Rita Ng

Veterinary clinical rotation student & content contributor

Bachelor of Veterinary Biology / Doctor of Veterinary Medicine, University of Sydney

Rita Ng is a fourth year Doctor of Veterinary Medicine student at the University of Sydney with a strong interest in small animal internal medicine and ultrasound. Through extensive clinical rotations across Sydney, Melbourne, and Hong Kong, she has built a broad foundation in diagnostics, surgery, and client care.

Clinical rotations across small animal, emergency, equine, and livestock practice
Special interest in internal medicine and diagnostic ultrasound
Treasurer, USYD Student Chapter of the American College of Veterinary Internal Medicine (ACVIM)

LEARN MORE ABOUT RITA

Ware, W. A., & Bonagura, J. D. (2021). Cardiovascular disease in companion animals : dog, cat and horse (Second edition.). CRC Press. https://www.taylorfrancis.com/books/9780429186639[↩][↩][↩][↩][↩][↩][↩][↩][↩]

Tilley, L. P. (2008). Manual of canine and feline cardiology (4th ed.). Elsevier Saunders.[↩]

MacDonald, K. A. (2006). Congenital Heart Diseases of Puppies and Kittens. The Veterinary Clinics of North America. Small Animal Practice, 36(3), 503–531. https://doi.org/10.1016/j.cvsm.2005.12.006[↩]

Kim, H.-T., Han, S.-M., Song, W.-J., Kim, B., Choi, M., Yoon, J., & Youn, H.-Y. (2017). Retrospective study of degenerative mitral valve disease in small-breed dogs: survival and prognostic variables. Journal of Veterinary Science (Suwŏn-Si, Korea), 18(3), 369–376. https://doi.org/10.4142/jvs.2017.18.3.369[↩]

Payne, J. R., Brodbelt, D. C., & Luis Fuentes, V. (2015). Cardiomyopathy prevalence in 780 apparently healthy cats in rehoming centres (the CatScan study). Journal of Veterinary Cardiology, 17, S244–S257. https://doi.org/10.1016/j.jvc.2015.03.008[↩]

Ware, W. A., Wendy A. Ware, John D. Bonagura, Bonagura, J. D., Scansen, B. A., & Brian A. Scansen. (2022). Murmurs and Abnormal Heart Sounds. In Cardiovascular Disease in Companion Animals (2nd ed., Vol. 1, pp. 225–236). CRC Press. https://doi.org/10.1201/9780429186639-13[↩]

Ljungvall, I., & Häggström, J. (2020). Approach to the Patient with Suspected Cardiovascular Disease. In D. S. Bruyette, N. Bexfield, J. D. Chretin, L. Kidd, S. Kube, C. Langston, T. J. Owen, M. A. Oyama, N. Peterson, L. V. Reiter, E. A. Rozanski, C. Ruaux, & S. M. F. Torres (Eds.), Clinical Small Animal Internal Medicine, Volume 1 (pp. 117–125). John Wiley & Sons, Inc. https://doi.org/10.1002/9781119501237.ch15[↩]

Côté, E., Edwards, N. J., Ettinger, S. J., Luis Fuentes, V., MacDonald, K. A., Scansen, B. A., Sisson, D. D., & Abbott, J. A. (2015). Management of incidentally detected heart murmurs in dogs and cats. Journal of Veterinary Cardiology, 17(4), 245–261. https://doi.org/10.1016/j.jvc.2015.05.001[↩]

Silva, G. P., Mendonça, D. do A., Camilo, E. J. F., Lima, N. da C., Damatis, M. P., de Souza, R. P., & Alberigi, B. (2026). Cardiovascular evaluation in overweight and obese dogs. Revista Brasileira de Medicina Veterinária, 48, e004426. https://doi.org/10.29374/2527-2179.bjvm004426[↩]

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Heart murmurs in Dogs and Cats: Everything you need to know

What Is a heart murmur in a dog or cat?

How are murmurs graded?

Is a grade VI murmur always more dangerous than a grade II?

What are the types of heart murmur?

What causes heart murmurs in pets?

Are all heart murmurs in growing pets a concern?

Adult dogs and cats

What is the most common cause of heart murmurs in adult dogs?

What is the most common cause of heart murmurs in cats?

Are heart murmurs more common in dogs or cats?

Why can heart murmurs in cats be difficult to interpret?

Does a heart murmur always mean it's because of the heart?

What signs should I watch for at home?

How do vets diagnose a heart murmur?

What is the most useful test for finding the cause of a murmur?

How are heart murmurs treated and managed?

How can you monitor your pet at home?

What Is the life expectancy for a pet with a heart murmur?

Should you worry if your vet detects a murmur at a routine check-up?

Can a heart murmur disappear on its own?

Heart murmurs in cats and dogs: key takeaways

Heart murmurs in Cats and Dogs: Frequently Asked Questions

Rita Ng

References

Pet Insurance

Pet insurance Info

More Links

Our Socials

About us

Work With Us

Media

Our Socials

Members Benefits

Become a Partner

More

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How We work with Vets

Work with your Clinic

Vet News

Our Socials

DOG

CAT

Pet Info

Our Socials

Pet Insurance Hub

Insurance

Policy Admin

Our Socials

Tail Talk Hub

Heart murmurs in cats and dogs:
key takeaways