Your veterinarian places a stethoscope against your dog’s chest, listens for a few seconds, and then says, “I hear a heart murmur.” Suddenly, your brain begins producing disaster-movie trailers. Is your dog in heart failure? Does exercise have to stop? Should you cancel every game of backyard fetch?

Take a breath. A heart murmur in dogs is an abnormal sound caused by turbulent blood flow in or near the heart. It is a clinical finding, not a complete diagnosis. Some murmurs are temporary and harmless, while others are the first clue to a congenital defect, a leaking heart valve, or a disease of the heart muscle.

The important questions are not simply, “Is there a murmur?” but “What is causing it, has the heart changed, and does the dog need treatment?” Answering those questions may require follow-up examinations, diagnostic imaging, and occasionally a visit to a veterinary cardiologist.

What Is a Heart Murmur in Dogs?

A normal canine heartbeat is often described as a steady “lub-dub.” Those sounds are produced largely by valves closing as blood moves through the heart’s four chambers. When blood becomes turbulent, a veterinarian may hear an additional swishing, blowing, humming, or whooshing sound between the normal beats.

Think of blood flowing through the heart like water moving through a garden hose. A wide, unobstructed hose produces relatively smooth flow. Narrow the hose, create a leak, or dramatically increase the water’s speed, and the flow becomes noisy. In the heart, that noise is called a murmur.

Veterinarians describe murmurs according to their loudness, location, timing within the cardiac cycle, pitch, duration, and sound quality. These features can provide clues, but a stethoscope alone usually cannot determine the complete cause or severity of the underlying condition.

A Heart Murmur Is Not the Same as Heart Failure

The words heart murmur, heart disease, and heart failure are often treated as interchangeable, but they mean different things.

• A heart murmur is an abnormal sound heard during an examination.
• Heart disease is a structural or functional problem involving the heart or major blood vessels.
• Congestive heart failure occurs when heart disease causes fluid to accumulate in places such as the lungs, chest, or abdomen.

A dog may have a murmur for years without developing heart failure. Conversely, some forms of heart disease, particularly early cardiomyopathy or rhythm disorders, may exist without a prominent murmur. The volume of the noise also does not always perfectly match the seriousness of the disease. A loud murmur deserves attention, but a quiet murmur should not automatically be dismissed as meaningless.

How Are Heart Murmurs Graded?

Veterinarians commonly grade canine heart murmurs on a scale from I to VI. The grade describes intensity, not a guaranteed prognosis.

Owners sometimes interpret a grade increase as proof that the heart is failing. It may indicate progression, but grading can also vary slightly depending on the dog’s heart rate, excitement level, body condition, chest shape, room noise, and the examiner. Diagnostic tests provide a much fuller picture than the grade alone.

Common Causes of Heart Murmurs in Dogs

Innocent or Physiologic Murmurs in Puppies

Some rapidly growing puppies develop a soft murmur even though the heart is structurally normal. These are often called innocent, physiologic, or flow murmurs. They are usually low-grade systolic murmurs and commonly disappear as the puppy matures, often by about six months of age.

That does not mean every puppy murmur should receive a cheerful shrug and a biscuit. Murmurs that are loud, continuous, heard most strongly on the right side, increasing in intensity, associated with symptoms, or still present at six months should be investigated. Congenital heart defects are uncommon, but early detection can significantly improve the options for certain puppies.

Myxomatous Mitral Valve Disease

Myxomatous mitral valve disease, commonly abbreviated MMVD, is one of the most frequent causes of an acquired heart murmur in dogs. The mitral valve separates the left atrium from the left ventricle. As the valve degenerates and thickens, it may not close tightly. Blood then leaks backward with each contraction, creating mitral regurgitation and a characteristic systolic murmur.

MMVD is particularly common in middle-aged and older small-breed dogs. Cavalier King Charles Spaniels have a well-recognized inherited susceptibility, but Dachshunds, Chihuahuas, Miniature Poodles, Maltese, and other small dogs may also be affected.

A veterinarian may hear the murmur months or even years before the owner notices coughing, breathing changes, or reduced stamina. This quiet period is exactly why routine examinations matter: the stethoscope may discover trouble before your dog files an official complaint.

Congenital Heart Defects

Congenital defects are present at birth, although they may not be identified until a puppy’s first wellness examination. Examples include:

• Patent ductus arteriosus, or PDA
• Pulmonic stenosis
• Subaortic stenosis
• Ventricular septal defects
• Malformations of the heart valves

Some congenital defects can be corrected or improved through surgery or catheter-based procedures. PDA, for example, creates an abnormal vessel connection that should close shortly after birth. Closing it early may prevent progressive heart enlargement and congestive heart failure.

Dilated Cardiomyopathy

Dilated cardiomyopathy, or DCM, is a disease in which the heart muscle becomes weak and the chambers enlarge. It occurs most often in large and giant breeds, including Doberman Pinschers, Great Danes, Boxers, and Irish Wolfhounds, although other dogs can develop it.

DCM may cause a murmur if enlargement stretches a valve enough to make it leak. However, an abnormal rhythm may be the first or more prominent finding. Some affected dogs appear normal during the early stages, while others develop weakness, exercise intolerance, fainting, coughing, rapid breathing, or sudden collapse.

Conditions Outside the Heart

Not every murmur begins with a defective valve. Severe anemia, fever, infection, pain, pregnancy, or other conditions that increase blood-flow speed can create a functional murmur in an otherwise structurally normal heart. Treatment focuses on correcting the underlying condition. Once normal circulation returns, the murmur may diminish or disappear.

Symptoms That May Accompany a Canine Heart Murmur

Many dogs with murmurs have no noticeable symptoms. They still chase squirrels, request second dinners, and become mysteriously unable to hear the word “bath.” When heart disease advances, however, owners may notice:

• Coughing, especially at night or after activity
• Faster breathing while resting or sleeping
• Labored breathing or excessive abdominal effort
• Reduced interest in walks or play
• Weakness or unusual fatigue
• Fainting or collapsing
• Pale, gray, or bluish gums
• Loss of appetite or unexplained weight loss
• A swollen abdomen caused by fluid accumulation
• Restlessness or difficulty getting comfortable at night

Coughing alone does not prove that a dog has heart failure. Airway disease, bronchitis, collapsing trachea, infections, and other respiratory conditions can produce similar symptoms. Middle-aged small dogs can even have both valve disease and airway disease at the same time, because apparently one medical puzzle was not enough. Chest imaging and other tests help distinguish the possibilities.

When Is It an Emergency?

Seek urgent veterinary care if your dog is struggling to breathe, breathing rapidly with obvious effort, collapsing repeatedly, unable to stand, coughing up foam or fluid, or developing blue, gray, or extremely pale gums. Do not force a dog in respiratory distress to walk. Keep the dog calm, minimize heat and excitement, and contact an emergency veterinary hospital while arranging transportation.

How Veterinarians Diagnose the Cause

Physical Examination and Medical History

The evaluation begins with listening to the heart and lungs, checking pulse quality, examining gum color, feeling the chest for vibrations, and looking for fluid retention. The veterinarian will also ask about coughing, breathing, fainting, exercise tolerance, appetite, medications, diet, and changes in behavior.

Chest X-Rays

Radiographs can show whether the heart is enlarged and whether fluid is present in the lungs or chest. They also provide valuable information about the airways, which is especially useful when coughing could have cardiac or respiratory causes.

Echocardiogram

An echocardiogram is an ultrasound examination of the heart. It allows a veterinarian or veterinary cardiologist to observe valve movement, chamber size, wall thickness, pumping function, and the direction and speed of blood flow. Doppler imaging can identify where abnormal flow is occurring and help measure the severity of an obstruction or leak.

For many structural heart conditions, echocardiography is the most informative diagnostic test. Most dogs tolerate it while awake, although a mild calming medication may occasionally be considered for extremely anxious patients.

Electrocardiogram and Rhythm Monitoring

An electrocardiogram, or ECG, records the heart’s electrical activity. It is useful for identifying arrhythmias but does not provide the same structural information as an echocardiogram. Dogs with intermittent fainting or suspected rhythm abnormalities may need a Holter monitor that records the heartbeat continuously for 24 hours or longer.

Blood Pressure and Laboratory Tests

Blood tests may look for anemia, infection, kidney function changes, electrolyte abnormalities, thyroid problems, or other conditions that can affect the cardiovascular system. Cardiac biomarkers such as NT-proBNP may help assess heart stress in selected cases, but they do not replace imaging or a complete clinical evaluation.

Does Every Dog With a Murmur Need Medication?

No. Veterinarians treat the disease and its stage, not merely the sound.

For dogs with MMVD, specialists often use a staging system developed by the American College of Veterinary Internal Medicine:

• Stage A: The dog is at risk but has no current structural disease.
• Stage B1: A murmur or valve abnormality is present without sufficient heart enlargement to justify cardiac medication.
• Stage B2: The dog remains free of heart-failure symptoms but has confirmed cardiac enlargement.
• Stage C: The dog currently has or previously experienced congestive heart failure.
• Stage D: Heart failure is advanced and difficult to control with standard treatment.

Dogs in Stage B1 are generally monitored rather than automatically medicated. For properly confirmed Stage B2 MMVD, veterinarians may prescribe pimobendan to delay the onset of congestive heart failure. Dogs in Stage C commonly require a combination of medications, potentially including a diuretic to remove excess fluid, pimobendan, and other drugs selected according to the individual patient.

These medicines should never be started, stopped, or adjusted without veterinary guidance. The correct plan depends on imaging findings, kidney function, blood pressure, symptoms, and response to treatmentnot on advice from a neighbor whose Pomeranian “had something heart-ish once.”

Living With a Dog That Has a Heart Murmur

A murmur does not automatically mean your dog must retire from normal life. Many dogs remain comfortable and active for years, particularly when disease is detected early and monitored appropriately.

Attend Recommended Rechecks

Your veterinarian may recommend examinations every six to twelve months for a stable, asymptomatic dog, with more frequent monitoring if the murmur changes or heart enlargement develops. The schedule should be personalized to the diagnosis and stage.

Track Sleeping Respiratory Rate

Count your dog’s breaths while deeply asleep, not immediately after a dream involving an imaginary mail carrier. One rise and fall of the chest equals one breath. Record the number regularly so you know your dog’s baseline. A persistent increase, especially when accompanied by effort, restlessness, or coughing, should be reported promptly. Many cardiologists use approximately 30 breaths per minute during sleep as a practical threshold, but follow the specific limit provided for your dog.

Keep Exercise Sensible

Unless the veterinarian recommends restriction, gentle and moderate activity may support weight control, muscle strength, and quality of life. Avoid forcing strenuous exercise in hot weather or pushing a dog that is tiring, coughing, slowing down, or becoming distressed.

Feed a Complete, Balanced Diet

Do not make dramatic dietary changes or add supplements without professional advice. Dogs receiving diuretics or other heart medications may need periodic kidney and electrolyte monitoring. Dogs with advanced disease may also need an individualized nutrition plan that supports appetite, muscle mass, and appropriate sodium intake.

What Is the Prognosis?

The outlook depends on the cause of the murmur, the degree of heart enlargement, the presence of arrhythmias, the dog’s age and overall health, and whether congestive heart failure has developed.

An innocent puppy murmur may disappear completely. A mild congenital defect may require only monitoring, while another defect may be correctable through a catheter-based procedure. Many dogs with early MMVD remain symptom-free for a long time. Dogs with heart failure need lifelong management, but medication and careful home monitoring can often preserve a good quality of life.

The murmur grade alone cannot provide a countdown clock. Diagnostic staging and changes over time are much more meaningful.

Experiences Dog Owners Commonly Face After a Murmur Is Found

The following composite examples reflect situations frequently encountered in veterinary practice. They are not descriptions of individual patients, but they show why two dogs with the same words on their medical chart may have very different experiences.

Experience One: The Puppy With a Soft Murmur

A family brings home an energetic ten-week-old mixed-breed puppy. During the first vaccination visit, the veterinarian hears a Grade II systolic murmur. The puppy is growing normally, has excellent energy, and has never coughed or fainted.

The family’s first reaction is panic. Their second reaction is an internet search, which rarely reduces panic because online searching has the emotional subtlety of a fire alarm. The veterinarian explains that some young puppies have innocent flow murmurs and recommends a careful recheck in several weeks.

At four months, the sound is softer. By six months, it is no longer detectable. No treatment was needed. The important part of this experience was not ignoring the finding. The puppy was monitored until the murmur either disappeared or proved persistent. Had it become louder or remained present, an echocardiogram would have been the logical next step.

Experience Two: The Senior Small Dog Who Seems Perfectly Fine

A nine-year-old Cavalier King Charles Spaniel arrives for an annual wellness examination. The owner reports no symptoms. The dog still enjoys walks, spins in circles before dinner, and considers every lap in the house to be legally available seating.

The veterinarian hears a new Grade III murmur over the left side of the chest. Because the breed and age make MMVD likely, chest radiographs and an echocardiogram are recommended. The ultrasound confirms a leaking mitral valve. The heart is mildly enlarged but has not reached the measurements used to define Stage B2 disease.

The result is Stage B1 MMVD. No heart medication is started. Instead, the owner receives a monitoring plan: rechecks, sleeping respiratory-rate tracking, weight control, and instructions to report coughing, breathing changes, fainting, or reduced stamina.

Eighteen months later, repeat imaging shows greater enlargement that now meets Stage B2 criteria. Medication is started before heart-failure symptoms appear. For the owner, this experience demonstrates an important point: choosing not to prescribe medication at the first visit was not neglect. It was stage-appropriate care, followed by treatment when the evidence supported it.

Experience Three: The Large Dog With Subtle Fatigue

A six-year-old Doberman has gradually become slower during walks. The change is easy to rationalize. Perhaps the weather is warmer. Perhaps the dog is finally becoming “mature,” a theory weakened by the fact that he still steals socks.

During an examination, the veterinarian detects an irregular rhythm and a soft murmur. An echocardiogram and ECG raise concern for dilated cardiomyopathy. A Holter monitor then records serious intermittent arrhythmias that would not have been captured during a five-minute clinic visit.

Treatment focuses on supporting heart function and managing the rhythm problem. Exercise recommendations are adjusted, and the owner learns to recognize weakness, collapse, and breathing difficulty as urgent warning signs.

This experience differs sharply from the puppy’s innocent murmur and the senior dog’s valve disease. The murmur is only one piece of the puzzle. Breed, symptoms, rhythm findings, imaging, and long-term monitoring are equally important.

The Emotional Experience Matters Too

Owners often leave the first appointment remembering only the phrase “heart murmur.” A written summary can help. Ask the veterinarian for the murmur grade, suspected cause, recommended tests, urgency level, activity guidance, recheck date, and signs that require emergency care.

It is also reasonable to request referral to a board-certified veterinary cardiologist when the murmur is loud, persistent, associated with symptoms, detected in a very young puppy, or accompanied by heart enlargement or an abnormal rhythm. A specialist consultation does not automatically mean the prognosis is poor. It means the family is gathering the clearest possible information before making decisions.

Conclusion

A heart murmur in a dog is a sound created by turbulent blood flow, not a diagnosis and not an automatic declaration of heart failure. It may be an innocent feature of puppyhood, the first sign of a congenital defect, or evidence of acquired conditions such as mitral valve disease or dilated cardiomyopathy.

The safest response is calm follow-through. Ask what the veterinarian heard, schedule recommended testing, watch for changes in breathing and stamina, and keep up with rechecks even when your dog appears perfectly healthy. Early detection gives veterinarians more time to identify the cause, establish a baseline, and begin treatment at the stage when it is most likely to help.

Note: This article is intended for general educational purposes and does not replace an examination, diagnosis, or treatment plan from a licensed veterinarian. The medical information was synthesized from veterinary clinical references, cardiology guidelines, and educational materials published by Merck Veterinary Manual, VCA Animal Hospitals, Cornell University College of Veterinary Medicine, UC Davis School of Veterinary Medicine, the University of Illinois College of Veterinary Medicine, Washington State University, the American Kennel Club, and the American College of Veterinary Internal Medicine.