A heart murmur in dogs is an unusual sound caused by turbulent blood flow, which a vet hears when listening to the heart with a stethoscope. Some murmurs are harmless, while others indicate an underlying heart condition that needs monitoring or treatment. Finding a murmur does not automatically mean your dog has heart failure or a shortened life expectancy.

Hearing that your dog has a heart murmur can be worrying, particularly if they seem perfectly healthy. The important questions are what is causing the murmur, whether the heart is functioning normally and whether the condition is likely to progress.

This guide explains the symptoms, causes, grades, genetic risks, treatment options and possible outcomes of heart murmurs in dogs.

What Does a Heart Murmur Mean in Dogs?

A normal heartbeat produces sounds associated with the opening and closing of heart valves. A murmur is an additional sound created when blood flow becomes turbulent.

Heart murmurs are not diseases themselves. They are findings that can have several possible explanations.

Some puppies develop innocent murmurs during growth without having structural heart disease. These often disappear as the puppy matures.

Other murmurs occur because blood is leaking through an abnormal valve or passing through a narrowed opening or congenital defect.

The significance depends on the cause, the dog's age, other examination findings and the results of any recommended investigations.

What Are the Symptoms of a Heart Murmur in Dogs?

Many dogs with heart murmurs have no visible symptoms, particularly during the early stages of heart disease. The murmur may be discovered during a routine vaccination appointment or annual health examination.

When an underlying heart condition begins affecting circulation or breathing, owners may notice:

• Coughing, sometimes during rest or at night.
• Reduced stamina or reluctance to exercise.
• Faster breathing while resting or sleeping.
• Difficulty breathing or increased breathing effort.
• Weakness or episodes of fainting.
• Unusual tiredness or reduced interest in activities.
• A swollen abdomen in some forms of advanced heart disease.

These symptoms are not specific to heart disease. For example, coughing may result from airway disease, while reduced activity can also occur with painful joints or other illnesses.

A dog that struggles to breathe, collapses or develops pale or blue-tinged gums needs emergency veterinary care.

What Causes Heart Murmurs in Dogs?

Heart murmurs can result from structural heart disease, changes in blood flow or certain conditions outside the heart.

Degenerative Mitral Valve Disease

Degenerative mitral valve disease is a common cause of heart murmurs in older, particularly small-breed dogs.

The mitral valve controls blood flow between the left atrium and left ventricle. When it becomes thickened and fails to close properly, blood can leak backwards, producing a murmur.

Some dogs remain stable for years. Others develop enlargement of the heart and eventually congestive heart failure.

Congenital Heart Defects

Congenital defects are present from birth. Examples include patent ductus arteriosus, pulmonic stenosis and subaortic stenosis.

Some defects are mild, while others interfere significantly with normal circulation. Certain conditions can be corrected or improved through specialist procedures.

Innocent or Physiological Murmurs

Some healthy puppies develop quiet murmurs associated with normal growth and blood-flow patterns.

These often disappear during the first few months of life. However, a persistent or concerning murmur still requires veterinary investigation.

Other Medical Conditions

Anaemia, fever and other conditions that change blood flow can sometimes produce murmurs without a primary structural heart defect.

This is another reason why identifying the cause matters more than simply knowing the murmur's grade.

Are Heart Murmurs in Dogs Hereditary?

Some conditions responsible for heart murmurs have an inherited component.

Degenerative mitral valve disease has a strong breed-associated genetic predisposition, particularly in Cavalier King Charles Spaniels. However, inheritance is complex and does not follow one simple pattern in every breed.

Certain congenital conditions, including subaortic stenosis and pulmonic stenosis, also occur more frequently in particular breeds, suggesting an inherited influence.

Not every murmur is hereditary. Innocent puppy murmurs and murmurs associated with anaemia or other illnesses may have no inherited cardiac cause.

Responsible breeding involves appropriate health screening, understanding family history and avoiding breeding dogs with relevant inherited cardiac disease.

Which Dog Breeds Are Most Prone to Heart Murmurs?

Any dog can develop a heart murmur, but certain breeds have recognised predispositions to conditions that cause them.

Cavalier King Charles Spaniel

Cavaliers have a particularly strong predisposition to degenerative mitral valve disease, which can develop at a younger age than in many other breeds.

Other Small Dog Breeds

Chihuahuas, Dachshunds, Miniature Poodles and several other small breeds are associated with degenerative valve disease, particularly as they age.

Boxer

Boxers have recognised susceptibility to certain congenital heart defects, including subaortic stenosis, which can produce a murmur.

Bulldog and French Bulldog

These breeds can be affected by congenital cardiac abnormalities, including pulmonic stenosis.

Golden Retriever and Newfoundland

These breeds are among those associated with subaortic stenosis, although not every affected dog develops severe disease.

Breed predisposition indicates increased risk, not certainty. A heart murmur should always be assessed individually rather than diagnosed from breed alone.

What Do Heart Murmur Grades 1 to 6 Mean?

Vets commonly describe heart murmur intensity using a scale from grade 1 to grade 6.

The grade describes how loud the murmur sounds, not necessarily how serious the underlying heart disease is.

In some conditions, particularly degenerative mitral valve disease, a louder murmur may be associated with more significant valve leakage. However, this relationship does not apply reliably to every heart condition.

How Is a Heart Murmur Diagnosed in Dogs?

A vet usually identifies a murmur by listening to the heart with a stethoscope, a process called auscultation.

The examination may reveal the murmur's location, timing, intensity and other clues about its possible cause.

Further investigations may include:

• Echocardiography: An ultrasound scan showing heart structures, valve movement and blood flow.
• Chest X-rays: Used to assess heart size and changes in the lungs.
• Electrocardiography: Records the heart's electrical activity and helps investigate abnormal rhythms.
• Blood tests: May identify anaemia, other illnesses or markers relevant to cardiac assessment.
• Blood pressure measurement: Helps identify additional cardiovascular concerns.

Echocardiography is particularly useful because it can distinguish different structural conditions and help determine whether treatment is needed.

Can a Dog Live a Normal Life With a Heart Murmur?

Yes. Many dogs with heart murmurs live comfortable, active lives, sometimes without ever developing significant heart-related symptoms.

The outlook depends on the underlying cause, severity, progression and response to treatment.

Positive Outcomes

An innocent puppy murmur may disappear completely. Some mild congenital abnormalities cause little long-term difficulty, while certain correctable defects have an excellent outlook following successful treatment.

Dogs with early degenerative valve disease may remain symptom-free for years, especially when monitored appropriately.

More Serious Outcomes

Some heart conditions progress and cause enlargement of the heart, abnormal rhythms, reduced exercise tolerance or congestive heart failure.

Heart failure occurs when the heart can no longer maintain circulation without harmful consequences, such as fluid accumulating in the lungs.

Advanced disease can shorten life expectancy, although medication may improve comfort and survival.

Because outcomes vary considerably, a murmur grade alone cannot provide a reliable prediction of lifespan.

How Are Heart Murmurs in Dogs Treated?

Treatment focuses on the condition causing the murmur rather than the sound itself.

Dogs with innocent murmurs may need no treatment. Dogs with mild structural disease may initially require monitoring rather than medication.

For degenerative mitral valve disease, veterinary cardiologists use a staging system to guide treatment.

Dogs with early disease and no significant heart enlargement may be monitored. Dogs with sufficiently advanced heart enlargement but no signs of heart failure may benefit from pimobendan, a prescription medication that can delay the onset of congestive heart failure in appropriately selected cases.

Dogs with heart failure often require additional medication, including diuretics to reduce fluid accumulation.

The ACVIM consensus guidelines provide evidence-based recommendations for diagnosis, staging and treatment of degenerative mitral valve disease.

Some congenital defects may be suitable for specialist surgical or catheter-based procedures. Treatment choices depend on the specific abnormality and individual circumstances.

How Can You Care for a Dog With a Heart Murmur at Home?

Home care should follow the diagnosis and your vet's recommendations.

Useful measures include maintaining a healthy body condition, providing appropriate activity, giving prescribed medication consistently and attending recommended follow-up appointments.

If your dog has confirmed heart disease, your vet may recommend monitoring their sleeping respiratory rate. Count breaths while your dog is genuinely asleep and record changes over time. A persistent increase above their normal pattern deserves veterinary advice.

Do not make sudden changes to exercise or start restrictive diets without discussing them with your vet.

For general weight-management advice, VetOptimal's guide to healthy weight and mobility in dogs

If your dog becomes less active, remember that heart disease is not the only possible explanation. Our guide to helping older dogs with stiff joints

When Is a Heart Murmur an Emergency?

A heart murmur itself is not necessarily an emergency, but certain symptoms require immediate action.

Seek emergency veterinary care if your dog has difficulty breathing, collapses, develops blue or very pale gums, or shows severe weakness.

Rapid breathing at rest, especially when accompanied by increased effort, can indicate a serious problem.

Do not wait for a routine appointment if your dog is struggling to breathe.

Frequently Asked Questions About Heart Murmurs in Dogs

How Long Can a Dog Live With a Heart Murmur?

Some dogs live a normal lifespan with a heart murmur, while others have conditions that shorten life expectancy. The underlying diagnosis and disease stage matter far more than the murmur grade alone.

Is a Grade 3 Heart Murmur Serious in Dogs?

A grade 3 murmur is moderately loud, but this does not establish how severe the underlying disease is. Your vet may recommend an echocardiogram to identify the cause and assess heart function.

Can a Heart Murmur in a Puppy Go Away?

Yes. Some puppies have innocent murmurs that disappear as they grow, often within the first six months. Persistent, loud or otherwise concerning murmurs require further investigation to rule out congenital heart disease.

Can Dogs With Heart Murmurs Still Go for Walks?

Many dogs with mild or stable heart conditions can continue enjoying walks. Exercise should reflect the diagnosis, symptoms and veterinary advice. Dogs with heart failure or reduced stamina may need a modified routine.

Does a Heart Murmur Mean My Dog Has Heart Failure?

No. A murmur may be detected years before heart failure develops, and some dogs never progress to heart failure. The two terms describe different findings.

Can Diet or Supplements Cure a Heart Murmur?

No food or supplement can reliably cure a heart murmur or repair a diseased heart valve. Appropriate nutrition supports general health, but structural heart disease requires veterinary assessment and, where indicated, medical or specialist treatment.

Are Heart Murmurs More Common in Older Dogs?

Degenerative valve disease becomes more common with age, particularly in small breeds. However, puppies can also have murmurs, including innocent murmurs and those caused by congenital heart defects.

Final Thoughts

A heart murmur in dogs is an important finding, but it is not automatically a sign of serious illness or a poor prognosis.

Some murmurs are harmless, while others indicate conditions that benefit from early diagnosis, monitoring or treatment.

Understanding the underlying cause is the most useful next step. With appropriate veterinary care, many dogs with heart murmurs continue enjoying comfortable, fulfilling lives.

This article provides general educational information and does not replace individual veterinary diagnosis, treatment or emergency care.