Heart Murmur Grades in Dogs: Symptoms, Diagnosis & Treatment
Understand heart murmur grades in dogs from Grade I to VI. Learn symptoms, diagnosis costs, treatment options, prognosis by stage, and when to see a vet.
If your veterinarian placed a stethoscope on your dog's chest and mentioned a "heart murmur," you're likely wondering what that means and how serious it is. A heart murmur is an abnormal sound caused by turbulent blood flow within the heart, detected during auscultation (listening with a stethoscope). Murmurs themselves are not a disease — they're a clinical sign pointing to an underlying condition, which can range from completely benign to life-threatening.
Heart murmurs are remarkably common in veterinary practice. Studies published in the Journal of Veterinary Internal Medicine estimate that approximately 30–40% of dogs will develop a heart murmur at some point in their lives. The prevalence climbs sharply with age: among dogs over 13 years old, mitral valve disease alone affects roughly 85% of small breeds. Understanding heart murmur grades in dogs is essential because the grade directly correlates with the intensity of turbulence — and often, though not always, with the severity of the underlying condition.
What Is a Heart Murmur in Dogs?
A heart murmur occurs when blood flow through the heart becomes turbulent instead of smooth and laminar. In a healthy canine heart, blood moves silently through four chambers separated by valves that open and close in precise sequence. When a valve leaks (regurgitation), fails to open fully (stenosis), or when there is an abnormal opening between chambers (septal defect), blood creates vibrations that produce an audible "whooshing" or "swishing" sound.
Veterinarians classify murmurs using a standardized grading scale originally adapted from the human medical Levine scale. The Merck Veterinary Manual describes the six-grade system used universally in small animal cardiology:
| Grade | Description | Clinical Significance |
|---|---|---|
| I | Very soft, heard only in quiet room after several seconds of listening | Often innocent/physiologic; common in puppies |
| II | Soft but readily heard with stethoscope | May be innocent or early pathologic |
| III | Moderately loud, no palpable thrill | Warrants investigation; may indicate structural disease |
| IV | Loud, no palpable thrill | Likely pathologic; echocardiogram recommended |
| V | Very loud with palpable thrill (vibration felt on chest wall) | Significant cardiac disease likely |
| VI | Very loud with thrill; audible with stethoscope partly off chest | Severe cardiac disease; often associated with heart failure |
A critical nuance many owners miss: murmur grade does not perfectly predict disease severity. A dog with a Grade III murmur from a small ventricular septal defect may live a completely normal lifespan, while a dog with a Grade IV murmur from dilated cardiomyopathy may be in active heart failure. The grade tells your vet how turbulent the blood flow sounds — the underlying cause determines the prognosis.
Heart Murmur Symptoms in Dogs: Early Warning Signs vs. Advanced Disease
Dogs are masters at hiding illness, and heart murmurs can be present for months or years before outward symptoms appear. The symptom timeline depends entirely on the underlying cause and how quickly the condition progresses. Below is a severity-organized checklist to help you monitor your dog.
Symptom Checklist by Severity
| Early Warning Signs (Grades I–III often asymptomatic) | Moderate Signs (Often Grades III–IV) | Advanced/Emergency Signs (Grades IV–VI) |
|---|---|---|
|
|
|
At-home monitoring tip: Count your dog's resting respiratory rate (RRR) while they sleep. Place your hand on their ribcage and count one rise-and-fall as one breath. A normal sleeping RRR is 15–25 breaths per minute. Consistently exceeding 30 breaths per minute at rest is a significant early indicator of congestive heart failure and warrants a veterinary visit within 48 hours.
Seek emergency veterinary care if your dog exhibits any of these red-flag symptoms:
- Difficulty breathing or open-mouth breathing (dogs should breathe through their nose at rest)
- Collapse or fainting (syncope)
- Blue, gray, or white gums or tongue
- Coughing up pink or frothy fluid
- Sudden inability to use hind legs (possible saddle thrombus, rare but critical)
- Extreme lethargy combined with rapid breathing
Risk Factors: Which Dogs Are Prone to Heart Murmurs?
Not all dogs carry equal risk for developing pathologic heart murmurs. Breed genetics, age, body condition, and even geographic location influence both the likelihood and type of underlying cardiac disease.
Key Risk Factors
| Breed | Small breeds (Cavalier King Charles Spaniels, Dachshunds, Miniature Poodles, Chihuahuas, Pomeranians) — highly predisposed to mitral valve disease (MVD). Cavaliers are so prone that the AKC recommends cardiac screening starting at age 1. Large breeds (Doberman Pinschers, Great Danes, Irish Wolfhounds, Boxers) — predisposed to dilated cardiomyopathy (DCM). |
| Age | Puppies under 6 months often have "innocent" murmurs that resolve by 16 weeks. Senior dogs over 8 years have dramatically higher rates of acquired valve disease. DCM typically presents in dogs aged 4–10 years. |
| Weight | Obesity increases cardiac workload and accelerates progression of existing heart disease. Dogs with a body condition score (BCS) of 7/9 or higher face compounded cardiovascular stress. |
| Genetics | Hereditary conditions: subaortic stenosis (Golden Retrievers, Rottweilers), pulmonic stenosis (English Bulldogs, Boxers), patent ductus arteriosus (Pomeranians, Collies). Responsible breeders screen for these via echocardiogram. |
| Diet | FDA investigation linked certain grain-free, boutique diets containing peas, lentils, and potatoes to DCM in breeds not traditionally predisposed. This diet-associated DCM remains under active study as of 2026. |
How Vets Diagnose the Cause of a Heart Murmur
Hearing the murmur is only step one. Your veterinarian needs to determine why turbulent blood flow exists — and that requires diagnostic imaging and laboratory work. Here is the typical diagnostic sequence you can expect:
- Physical Examination & Auscultation ($50–$95)
Your vet listens with a stethoscope, noting the murmur's grade, timing (systolic vs. diastolic), location on the chest (left vs. right, which valve area), and character (blowing, harsh, musical). This initial assessment guides next steps. - Thoracic Radiographs / X-rays ($150–$350)
Two or three views of the chest reveal heart size (cardiomegaly), pulmonary vessel patterns, and fluid accumulation in the lungs (pulmonary edema) or chest cavity (pleural effusion). The vertebral heart score (VHS) is a standardized measurement used to objectively assess cardiac enlargement. - Echocardiogram ($350–$700)
This is the gold standard for diagnosing the cause of a heart murmur. An ultrasound of the heart visualizes valve structure, chamber dimensions, wall thickness, and blood flow direction/speed via Doppler imaging. A board-certified veterinary cardiologist often performs this — expect a referral for the most accurate assessment. The echocardiogram is the only test that definitively identifies conditions like mitral valve regurgitation severity, DCM, or congenital defects. - Electrocardiogram / ECG ($75–$200)
Measures the heart's electrical activity to identify arrhythmias (irregular rhythms) that may accompany structural disease. Particularly important for breeds prone to atrial fibrillation (Irish Wolfhounds) or ventricular arrhythmias (Boxers, Dobermans). - Blood Work: CBC, Chemistry Panel, NT-proBNP ($120–$300)
A complete blood count and chemistry panel assess organ function before starting medications. The NT-proBNP cardiac biomarker test (approximately $85–$150) measures a hormone released when heart muscle stretches — elevated levels correlate with cardiac disease severity and help distinguish cardiac from respiratory causes of coughing. - Blood Pressure Measurement ($40–$80)
Systemic hypertension can worsen murmurs and is a comorbidity that requires concurrent management. Measured via Doppler or oscillometric cuff, similar to human blood pressure checks.
Total diagnostic cost range: $785–$1,725 for a comprehensive cardiac workup. Not all tests are needed for every dog — a young puppy with a Grade I murmur may only need a recheck in 3 months, while a senior Cavalier with a Grade IV murmur will likely need the full panel.
Common Causes Behind Each Heart Murmur Grade
Understanding what typically causes murmurs at each grade helps set expectations for your dog's diagnosis:
| Grade | Common Causes | Typical Age of Onset |
|---|---|---|
| I–II | Innocent/physiologic murmurs (puppies), anemia, fever, pain, hyperthyroidism, early-stage mitral valve disease | Puppies 6–16 weeks; seniors 7+ for MVD |
| III | Moderate mitral regurgitation, mild subaortic stenosis, mild DCM, patent ductus arteriosus | Varies: congenital at any age; acquired 5+ years |
| IV | Significant mitral regurgitation, moderate-to-severe DCM, moderate congenital defects | Typically 6+ years for acquired; congenital variable |
| V–VI | Severe mitral or tricuspid regurgitation with chamber enlargement, advanced DCM, severe congenital stenosis, ruptured chordae tendineae | Usually older dogs with progressive disease; congenital in young dogs |
Treatment Options for Heart Murmurs in Dogs
The murmur itself is not treated — the underlying condition is. Treatment strategies depend on the diagnosis, disease stage, and your dog's clinical signs. According to the AVMA, early intervention significantly improves quality of life and longevity.
Medical Management
- Pimobendan (Vetmedin): A positive inotrope and vasodilator that improves heart contractility and reduces workload. Standard for MVD Stage B2 and DCM. Cost: $30–$90/month depending on dose.
- ACE Inhibitors (Enalapril, Benazepril): Reduce blood pressure and cardiac afterload. Cost: $15–$50/month.
- Furosemide (Lasix/Salix): A diuretic that removes excess fluid from lungs and abdomen during congestive heart failure. Cost: $10–$35/month.
- Spironolactone: A potassium-sparing diuretic used alongside furosemide to reduce cardiac fibrosis. Cost: $15–$40/month.
- Sotalol, Mexiletine, or Atenolol: Anti-arrhythmic drugs for dogs with concurrent rhythm disturbances. Cost: $20–$60/month.
Surgical & Interventional Options
- PDA Occlusion: Patent ductus arteriosus can be closed via catheter-based coil or ACDO device placement. Success rate: >95%. Cost: $3,000–$6,000. Curative if performed before heart failure develops.
- Balloon Valvuloplasty: For severe pulmonic stenosis, a balloon catheter stretches the narrowed valve. Improves prognosis significantly. Cost: $4,000–$8,000.
- Valve Repair/Replacement: Mitral valve repair surgery (V-Clamp, open-heart repair) is available at a limited number of specialty centers. Cost: $10,000–$25,000+. Still relatively uncommon in veterinary medicine but expanding.
- Pacemaker Implantation: For complete atrioventricular block or sick sinus syndrome. Cost: $4,000–$8,000.
Supportive care includes prescription cardiac diets (e.g., Hill's h/d, Royal Canin Cardiac, Purina Pro Plan Veterinary Supplements CardioCare), omega-3 fatty acid supplementation (EPA/DHA at 30–40 mg/kg combined daily), taurine supplementation for breeds at risk of taurine-deficient DCM (Cocker Spaniels, Golden Retrievers — 500–1,000 mg twice daily for medium-large dogs), and controlled exercise programs.
Prognosis by Heart Murmur Grade and Underlying Cause
Prognosis varies enormously depending on the cause, not just the grade. Here is a realistic breakdown based on current veterinary cardiology data:
| Scenario | Typical Murmur Grade | Prognosis | Expected Survival |
|---|---|---|---|
| Innocent puppy murmur | I–II | Excellent — resolves spontaneously | Normal lifespan |
| Early MVD (Stage B1, no enlargement) | I–III | Good — monitor every 6–12 months | Often normal lifespan; may never progress to heart failure |
| MVD Stage B2 (enlargement, no failure) | III–IV | Fair — pimobendan delays failure onset by ~15 months (EPIC study) | Median 2–4 years before CHF onset with treatment |
| MVD with congestive heart failure (Stage C) | IV–VI | Guarded — manageable but not curable | Median 6–18 months with multi-drug therapy; some dogs live 2–3+ years |
| DCM (Doberman, Great Dane) | III–V | Guarded to poor once symptomatic | Median 3–6 months post-CHF diagnosis; occult (pre-symptomatic) may live 1–3 years with early pimobendan |
| PDA (surgically corrected) | III–V pre-op | Excellent if corrected early | Normal lifespan expected |
| Diet-associated DCM (reversed) | II–IV | Good to excellent with diet change + taurine + time | Many dogs show significant echocardiographic improvement within 6–12 months of switching to AAFCO-compliant diet |
Home Care and Daily Management for Dogs with Heart Murmurs
Once your dog is diagnosed and treatment begins, your daily management plays a direct role in their quality of life and longevity. Here is a practical framework:
Daily Monitoring Routine
- Resting respiratory rate (RRR): Count breaths per minute while your dog sleeps. Log this daily in a notebook or app. Alert your vet if RRR consistently exceeds 30 breaths/minute or shows a rising trend over several days.
- Weight tracking: Weigh your dog weekly on the same scale. Sudden weight gain (1–2 lbs in 24–48 hours in a small dog) may indicate fluid retention. Weight loss may signal cardiac cachexia.
- Cough log: Note frequency, duration, and timing of coughing episodes. Video record episodes for your vet — a 10-second clip on your phone is diagnostically valuable.
- Activity tolerance: Track walk duration and note when your dog starts lagging, sitting down, or refusing to continue.
Lifestyle Adjustments
- Exercise: Continue short, controlled walks (10–20 minutes, 2–3 times daily is often better than one long walk). Avoid intense exertion, especially in heat. Swimming is low-impact but only if your dog enjoys it and can exit the water easily.
- Diet: Feed a veterinary-recommended cardiac diet or a well-established brand with AAFCO feeding trial data. Sodium restriction becomes important in Stage C/D heart failure — avoid high-sodium treats (jerky, deli meats, cheese). Target sodium intake: <50 mg per 100 kcal for dogs in CHF.
- Dental care: Poor dental health can introduce bacteria into the bloodstream that colonize damaged heart valves (endocarditis). Daily tooth brushing and professional cleanings (with cardiac-safe anesthesia protocols) are important.
- Stress reduction: Minimize stressful situations. Use positive reinforcement training and calming enrichment (snuffle mats, lick mats, puzzle feeders) rather than high-arousal play for dogs with advanced disease.
- Temperature control: Keep your home cool (68–72°F / 20–22°C). Heat stress significantly worsens cardiac workload. Never leave a cardiac dog in a car or hot yard.
Medication Management
Administer all medications on schedule. Pimobendan must be given on an empty stomach (1 hour before or 2 hours after food) for proper absorption. Furosemide timing should account for increased urination — avoid giving the last dose right before bedtime if possible. Never stop cardiac medications abruptly without veterinary guidance, as this can precipitate acute heart failure.
Cost of Heart Murmur Diagnosis and Treatment in Dogs
Budgeting for cardiac care is a practical reality for owners. Here is a realistic cost breakdown based on 2026 US veterinary pricing:
| Expense Category | Low Estimate | High Estimate | Frequency |
|---|---|---|---|
| Initial exam & murmur detection | $50 | $95 | One-time |
| Chest X-rays (2–3 views) | $150 | $350 | Every 6–12 months |
| Echocardiogram (cardiologist) | $350 | $700 | Every 6–12 months |
| ECG | $75 | $200 | As needed |
| Blood work + NT-proBNP | $120 | $300 | Every 6–12 months |
| Monthly medications (multi-drug CHF) | $70 | $250 | Monthly, ongoing |
| Emergency CHF crisis hospitalization | $1,500 | $5,000+ | Per episode |
| Surgical intervention (PDA, valve) | $3,000 | $25,000+ | One-time (if applicable) |
First-year total (diagnosis + ongoing medical management): $1,200–$3,500 for most dogs with acquired heart disease managed medically. Pet insurance with illness coverage can reimburse 70–90% of these costs, but most policies exclude pre-existing conditions — enrolling before a murmur is detected is critical.
Prevention Strategies
While not all heart murmurs are preventable, several strategies reduce risk or delay progression:
- Feed an established, AAFCO-compliant diet: Avoid boutique, grain-free, or exotic-ingredient diets that have been associated with diet-associated DCM. Look for brands that employ full-time veterinary nutritionists and conduct AAFCO feeding trials (not just formulation analysis). Purina, Hill's, Royal Canin, and Iams have the most robust feeding trial data.
- Maintain ideal body condition: Keep your dog at a BCS of 4–5 out of 9. Every extra pound of body weight increases cardiac workload.
- Annual veterinary exams: Murmurs are often detected at routine wellness visits before symptoms appear. Senior dogs (7+ years) should have exams every 6 months.
- Breed-specific screening: If you own a predisposed breed, ask your vet about baseline echocardiograms. The Orthopedic Foundation for Animals (OFA) maintains a cardiac registry for breeding dogs.
- Dental hygiene: Daily brushing and professional cleanings reduce the risk of bacterial endocarditis seeding on abnormal valves.
- Heartworm prevention: Heartworm disease (transmitted by mosquitoes) causes pulmonary hypertension and right-sided heart murmurs. Monthly preventive medication (Heartgard, Interceptor, Revolution) costs $8–$25/month and is far cheaper than the $1,000–$3,000+ treatment for adult heartworm infection.
Frequently Asked Questions
What is a heart murmur in dogs?
A heart murmur is an abnormal sound caused by turbulent blood flow within the heart, detected by stethoscope. It is a clinical sign, not a disease itself, and indicates an underlying condition ranging from benign (innocent puppy murmurs) to serious (valve disease, cardiomyopathy, congenital defects).
Can a heart murmur in dogs be cured?
It depends on the cause. Innocent puppy murmurs resolve on their own. Congenital defects like patent ductus arteriosus can be surgically corrected with >95% success. Acquired conditions like mitral valve disease and dilated cardiomyopathy cannot be cured but can be managed with medication for months to years. Diet-associated DCM may partially or fully reverse with dietary correction.
How much does heart murmur treatment cost for dogs?
Initial diagnostic workup ranges from $785–$1,725. Ongoing monthly medication costs $70–$250 for dogs in heart failure. Emergency hospitalization for a CHF crisis costs $1,500–$5,000+. Surgical correction of congenital defects ranges from $3,000–$25,000 depending on the procedure.
What is the life expectancy of a dog with a heart murmur?
Life expectancy varies enormously. Dogs with innocent murmurs or early-stage disease often live a normal lifespan. Dogs diagnosed with MVD in Stage B2 have a median 2–4 years before heart failure onset. Once in congestive heart failure (Stage C), median survival is 6–18 months with treatment, though some dogs live 2–3+ years. DCM in Dobermans carries a shorter prognosis of 3–6 months once symptomatic.
Which breeds are most prone to heart murmurs?
Small breeds most prone to mitral valve disease: Cavalier King Charles Spaniels, Dachshunds, Miniature Poodles, Chihuahuas, Pomeranians, and Shih Tzus. Large breeds most prone to dilated cardiomyopathy: Doberman Pinschers, Great Danes, Irish Wolfhounds, Boxers, and Cocker Spaniels. Congenital defects vary: Golden Retrievers (subaortic stenosis), English Bulldogs (pulmonic stenosis), Pomeranians (PDA).
Should I restrict my dog's activity if they have a heart murmur?
For low-grade murmurs without clinical signs, normal activity is usually fine — your vet will advise. For dogs with moderate-to-severe disease or heart failure symptoms, switch to shorter, gentler walks (10–20 minutes, multiple times daily). Avoid intense exercise, especially in heat. Let your dog set the pace and stop when they want to rest.
My puppy has a heart murmur — should I be worried?
Not necessarily. Innocent murmurs are very common in puppies, affecting an estimated 15–30% of puppies at their first vet visits. These are typically Grade I–II and resolve by 12–16 weeks of age as the cardiovascular system matures. Your vet will likely recommend a recheck at 4–6 months. If the murmur persists beyond 6 months or is Grade III+, further investigation with an echocardiogram is warranted to rule out congenital heart defects.
Understanding heart murmur grades in dogs empowers you to have informed conversations with your veterinarian, ask the right questions, and make decisions that maximize your dog's quality and quantity of life. If your dog has been diagnosed with a murmur, the single most important step is completing the diagnostic workup — knowing the underlying cause transforms uncertainty into an actionable plan.
Dr. Hannah Wickes
All our authors care for dogs every day — read more of their work on the authors page.
