Dog Heart Murmur: Grades, Causes & What It Means for Your Dog

Last updated: May 6, 2026

Hearing that your dog has a heart murmur can be an unsettling experience. The word “murmur” sounds vague, and the immediate questions — is this serious? does my dog need medication? will this shorten their life? — can feel overwhelming. The truth is that a dog heart murmur is not a disease in itself. It is a physical finding, an abnormal sound that a veterinarian hears through a stethoscope when listening to your dog’s heart. What matters most is understanding what is causing that sound, how severe it is, and what it means for your dog’s daily life and long-term health.

This guide covers everything you need to know about heart murmurs in dogs — from grading scales and common causes to diagnosis, treatment, and what day-to-day life looks like for a dog living with a murmur.

What Is a Heart Murmur in Dogs?

A heart murmur is an abnormal whooshing or swishing sound produced by turbulent blood flow within the heart. In a healthy heart, blood moves smoothly through the chambers and valves, and the only sounds are the normal “lub-dub” of the valves closing. When something disrupts that flow — a leaky valve, a narrowed opening, an abnormal connection between chambers, or thinner-than-normal blood — the turbulence creates an audible vibration. A dog heart murmur is characterized by its timing in the cardiac cycle, its location on the chest, and its intensity, which is what the grading system measures.

Heart Murmur Grades in Dogs: The 1-6 Scale

Veterinarians grade heart murmurs on a scale from 1 to 6 based on loudness. Importantly, loudness does not always correlate directly with severity of the underlying disease — a grade 3 murmur from a slowly progressing condition may be less urgent than a grade 2 murmur in a dog already showing symptoms. That said, higher grades generally warrant more thorough investigation.

• Grade 1 — barely audible, even in a quiet room. Often an incidental finding that may not indicate significant disease.
• Grade 2 — soft but consistently audible with a stethoscope. Common in dogs with early valve changes or benign flow murmurs.
• Grade 3 — moderately loud, easily heard when the stethoscope is placed on the chest. Most veterinarians recommend diagnostic workup at this level.
• Grade 4 — loud, may radiate beyond its point of maximum intensity. Typically indicates more significant structural heart changes.
• Grade 5 — very loud with a palpable vibration (precordial thrill) felt through the chest wall. Generally indicates significant cardiac pathology.
• Grade 6 — the loudest grade, audible even with the stethoscope slightly lifted off the chest. Associated with severe structural heart disease.

Innocent vs Pathological Heart Murmurs

Not every heart murmur indicates disease, and this distinction is one of the most important things for dog owners to understand.

Innocent murmurs — also called physiologic or benign flow murmurs — are commonly heard in puppies between six and sixteen weeks of age. These are usually grade 1 or 2, caused by normal turbulence in a young, rapidly growing heart rather than by any structural defect. They resolve on their own by four to five months of age. Your veterinarian will likely recommend rechecking at subsequent vaccine appointments to confirm resolution.

Pathological murmurs are caused by an actual structural or functional abnormality — valve disease, congenital defects, or diseases of the heart muscle. A pathological murmur does not mean your dog is in immediate danger, but it does mean there is an underlying condition that needs to be identified and monitored. The distinction between innocent and pathological murmurs is made through diagnostic testing, not by the sound alone.

Common Causes of Heart Murmurs in Dogs

The list of conditions that can produce a dog heart murmur is broad, but several causes account for the majority of cases seen in clinical practice.

Mitral Valve Disease (MVD)

Mitral valve disease (MVD), also known as myxomatous mitral valve disease, is the single most common cause of heart murmurs in dogs — accounting for roughly 75 percent of all canine heart disease. The mitral valve gradually degenerates, its leaflets becoming thickened and unable to close tightly. Blood leaks backward into the left atrium each time the ventricle contracts, producing the characteristic systolic murmur. MVD is progressive, typically beginning with a soft murmur and no symptoms, then advancing over months to years through increasing grades, heart enlargement, and in some dogs, congestive heart failure. The rate of progression varies enormously — some dogs live for years with a stable murmur while others progress more rapidly.

Dilated Cardiomyopathy (DCM)

In DCM, the walls of the ventricles become thin and weak and the chambers dilate, impairing the heart’s ability to pump effectively. DCM primarily affects large and giant breed dogs and tends to progress more quickly than MVD. Unlike valve disease, DCM may present with arrhythmias, exercise intolerance, or sudden collapse before a murmur is detected.

Congenital Heart Defects

Some dogs are born with structural abnormalities of the heart. The most common congenital defects that produce murmurs include:

• Patent ductus arteriosus (PDA) — a fetal blood vessel that should close at birth but remains open, creating a continuous murmur
• Pulmonic stenosis — narrowing of the pulmonic valve or the area around it, restricting blood flow to the lungs
• Subaortic stenosis (SAS) — narrowing below the aortic valve, which creates turbulent blood flow as the left ventricle empties
• Ventricular septal defect (VSD) — a hole in the wall between the two ventricles that allows blood to shunt between them

Congenital murmurs are typically detected at the first puppy wellness visit and persist rather than resolving like innocent murmurs. Some congenital defects are mild and require only monitoring, while others — particularly moderate-to-severe PDA — may require surgical correction.

Anemia

Anemia — a reduction in red blood cells or hemoglobin — can produce a heart murmur even in the absence of any structural heart disease. When the blood is thinner and less viscous than normal, it flows more turbulently through the heart, creating an audible murmur. Anemia-related murmurs are typically soft (grade 1 to 3) and resolve once the underlying cause of the anemia is treated. Causes of anemia in dogs include blood loss, immune-mediated red cell destruction, tick-borne diseases, and chronic kidney disease.

Symptoms to Watch For

Many dogs with heart murmurs show no symptoms at all — the murmur is discovered incidentally during a routine exam. As the underlying condition progresses, however, signs may develop:

• Coughing — especially at night or after lying down, caused by fluid accumulation or an enlarged heart pressing on the airways
• Exercise intolerance — tiring more quickly on walks, reluctance to play, or lagging behind on activities they previously enjoyed
• Rapid or labored breathing — an increased resting respiratory rate (above 30-40 breaths per minute while sleeping) is one of the earliest and most reliable indicators of developing heart failure
• Fainting or collapse — brief episodes of weakness or loss of consciousness, particularly during exertion or excitement
• Abdominal distension — fluid accumulation in the abdomen (ascites), more common with right-sided heart failure
• Decreased appetite and weight loss — advanced heart disease can cause reduced appetite, muscle wasting, and overall decline in body condition
• Restlessness at night — difficulty settling, pacing, or changing positions frequently, often related to breathing difficulty

If your dog has a known murmur and develops any of these signs, contact your veterinarian promptly. Early intervention when symptoms first appear can significantly improve outcomes.

How Heart Murmurs Are Diagnosed

Detecting a heart murmur is straightforward — a veterinarian hears it through a stethoscope during a physical exam. But identifying the cause and assessing the severity requires additional diagnostic tools.

Echocardiogram (cardiac ultrasound) is the gold standard. This non-invasive study lets the veterinarian visualize the heart in real time — assessing chamber size and function, examining valves for structural changes, measuring blood flow direction and velocity with Doppler, and identifying congenital defects. An echocardiogram reveals both the cause of the murmur and how well the heart is compensating. Additional tests that may be recommended include:

• Chest radiographs (X-rays) — to assess heart size, look for pulmonary edema (fluid in the lungs), and evaluate the pulmonary vessels
• Electrocardiogram (ECG) — to detect arrhythmias that may accompany structural heart disease
• Blood pressure measurement — high blood pressure can worsen valve regurgitation and contribute to murmur progression
• Blood work — including cardiac biomarkers like proBNP, which can help distinguish between cardiac and non-cardiac causes of symptoms, plus a complete blood count to rule out anemia

Treatment by Cause

Treatment for a dog heart murmur depends entirely on the underlying condition, its severity, and whether symptoms are present. There is no single treatment for “a murmur” — the murmur is the sign, not the disease.

Mitral Valve Disease

In preclinical stages (murmur present, no symptoms, no significant enlargement), treatment may not be needed. The EPIC trial showed that pimobendan can delay heart failure onset when started in dogs with significant preclinical heart enlargement. Once congestive heart failure develops, treatment typically includes furosemide (a diuretic), pimobendan, and an ACE inhibitor such as enalapril or benazepril.

Dilated Cardiomyopathy

Pimobendan is a cornerstone of DCM treatment, often combined with diuretics and ACE inhibitors. Anti-arrhythmic medications may be added for dangerous heart rhythms. Some cases related to taurine deficiency may partially improve with dietary correction and supplementation.

Congenital Defects

Some congenital defects, particularly PDA, are best treated with surgical or interventional correction (catheter-based occlusion). When performed early, the prognosis after PDA repair is excellent and often curative. Pulmonic stenosis may be treated with balloon valvuloplasty in moderate-to-severe cases. Mild congenital defects that are not causing symptoms or heart enlargement may be managed with monitoring alone.

Anemia-Related Murmurs

Treatment targets the cause of the anemia rather than the heart. Once red blood cell levels return to normal, the murmur resolves. This may involve blood transfusions, immunosuppressive therapy, treatment for tick-borne infections, or management of chronic kidney disease, depending on the underlying cause.

Dog Breeds at Risk for Heart Murmurs

While heart murmurs can occur in any dog, certain breeds carry genetic predispositions to the cardiac conditions that produce them.

Breeds predisposed to mitral valve disease:

• Cavalier King Charles Spaniels — the breed most strongly associated with early-onset MVD, with nearly all affected by age ten
• Dachshunds — commonly develop MVD in middle to senior years
• Miniature and Toy Poodles — small size correlates with higher MVD risk
• Chihuahuas — frequently affected, often diagnosed at routine wellness exams
• Cocker Spaniels — both American and English varieties carry elevated risk
• Maltese, Yorkshire Terriers, and Pomeranians — small breed predisposition

Breeds predisposed to dilated cardiomyopathy:

• Doberman Pinschers — one of the breeds most severely affected by DCM
• Great Danes — giant breed size and genetic predisposition combine for high risk
• Boxers — prone to arrhythmogenic right ventricular cardiomyopathy, a related condition
• Irish Wolfhounds — frequently affected, often diagnosed in middle age
• Newfoundlands — both DCM and subaortic stenosis occur at elevated rates

If you are considering bringing a dog of any of these breeds into your family, you can explore options through our adoption page or learn more about breed-specific traits and health profiles in the dog breeds directory.

Monitoring a Heart Murmur Over Time

For dogs with stable, asymptomatic murmurs, regular monitoring is the cornerstone of management. The goal is to detect progression early so that treatment can begin at the optimal time — neither too early (when it would provide no benefit) nor too late (when significant damage has already occurred).

A typical monitoring plan includes:

• Veterinary rechecks every 6-12 months — more frequently if the murmur is moderate to severe or progressing
• Periodic echocardiograms — to track changes in heart size and function over time, typically annually for significant murmurs
• Chest radiographs — as needed to assess heart size and check for early signs of fluid accumulation
• Resting respiratory rate monitoring at home — counting your dog’s breaths per minute while they are sleeping provides a simple, reliable way to detect early heart failure between veterinary visits; a sustained increase above 30-40 breaths per minute warrants prompt veterinary attention

Your veterinarian or veterinary cardiologist will tailor the monitoring schedule to your dog’s specific condition, breed risk factors, and rate of progression.

When Does Medication Start?

The answer depends on the condition and its stage. For MVD — the most common cause — current guidelines follow the ACVIM staging system:

• Stage A — breeds at risk but no murmur detected. No treatment needed, just awareness and regular screening.
• Stage B1 — murmur present but the heart is not significantly enlarged on imaging. No medication recommended. Monitoring continues.
• Stage B2 — murmur present with significant heart enlargement (left atrium and left ventricle) confirmed on echocardiogram and radiographs, but no clinical symptoms yet. This is the stage at which pimobendan is started, based on the EPIC trial results showing it delays onset of heart failure by a median of fifteen months.
• Stage C — congestive heart failure has developed (symptoms like coughing, breathing difficulty, exercise intolerance). Multiple medications are started, including furosemide, pimobendan, and an ACE inhibitor.
• Stage D — refractory heart failure that is no longer responding adequately to standard therapy. Additional or higher-dose medications are used, and quality-of-life considerations become central to decision-making.

For DCM, pimobendan is often started at diagnosis because the disease progresses more rapidly. The key takeaway is that not every dog with a murmur needs medication — many live comfortably for years with monitoring alone. Medication starts when the heart begins changing in ways that put the dog at risk.

Living with a Heart Murmur Dog

A heart murmur diagnosis does not mean your dog’s quality of life is over. Many dogs with murmurs continue to live happy, active lives for years. How you manage their daily routine, however, can make a meaningful difference in their comfort and longevity.

Exercise. Dogs with low-grade murmurs and no symptoms generally do not need exercise restrictions — let your dog set the pace. Dogs in early heart failure benefit from shorter, gentler walks. Avoid exercising in extreme heat and watch for excessive panting or fatigue.

Diet. Sodium restriction is commonly recommended for dogs in heart failure since excess sodium promotes fluid retention. Maintaining a healthy body weight matters — excess weight increases cardiac workload, while significant weight loss (cardiac cachexia) signals advanced disease. Omega-3 fatty acids and taurine supplementation may be recommended in certain cases.

Medication compliance. Cardiac medications work best at regular intervals, and missed doses can cause setbacks. Many need to be given twice daily at twelve-hour intervals. Setting reminders or tying medication to a fixed daily routine helps ensure consistency.

Home monitoring. Count your dog’s resting respiratory rate while they sleep — chest rises in thirty seconds, multiplied by two. Record this regularly. A sustained increase above 30-40 breaths per minute is an early warning sign of developing heart failure and warrants prompt veterinary attention.

If you are thinking about adopting a dog and want to learn more about breed-specific health considerations, visit our adoption page to meet dogs looking for homes, or explore the dog breeds directory for detailed breed profiles.

Frequently Asked Questions

Can a dog live a normal life with a heart murmur?

Yes. Dogs with low-grade murmurs and no heart enlargement often require nothing more than regular monitoring and live comfortably for years. Even dogs that eventually need medication can maintain good quality of life with proper management. Prognosis depends on the underlying cause, rate of progression, and how early the condition is detected.

How long can a dog live with a grade 3 heart murmur?

A grade 3 heart murmur alone does not determine life expectancy — the underlying cause and the state of the heart matter far more than the number on the grading scale. A dog with a grade 3 murmur caused by early mitral valve disease and a heart that is still normal in size may live for many years. Some dogs with MVD have murmurs for five to eight years or longer before developing any symptoms. Regular veterinary monitoring and timely intervention when heart changes occur are the most important factors in maximizing longevity.

Is a heart murmur in a puppy serious?

It depends on the type. Innocent (physiologic) murmurs are extremely common in puppies and typically resolve by four to five months of age. These are not a cause for concern. However, a murmur that persists beyond five months of age, is moderate to loud (grade 3 or higher), or is accompanied by other signs like poor growth, exercise intolerance, or blue-tinged gums may indicate a congenital heart defect and should be investigated with an echocardiogram.

What does a heart murmur sound like in a dog?

A heart murmur sounds like a whooshing, swishing, or blowing sound heard between or overlapping with the normal heart sounds. It is caused by turbulent blood flow and is distinct from the clear, crisp “lub-dub” of a healthy heart. The specific character of the sound — its timing, pitch, and quality — gives the veterinarian clues about which structure in the heart is involved.

Should I adopt a dog with a heart murmur?

A heart murmur should not automatically disqualify a dog from adoption. Many shelter dogs have low-grade murmurs that may never progress. Get a clear picture of the cause through proper diagnostics so you can make an informed decision. Dogs with heart conditions make wonderful companions and benefit enormously from the stability of a loving home.