Dog Heart Murmur: Symptoms, Grades, Diagnosis & Treatment Guide

Hearing the words "heart murmur" during a routine vet visit can stop any dog owner in their tracks. But before panic sets in, it helps to understand exactly what you're dealing with. A dog heart murmur is an abnormal sound heard through a stethoscope, caused by turbulent blood flow within or around the heart. It is not a disease itself — it's a clinical sign that may point to an underlying cardiac condition, or in some cases, nothing serious at all.

Heart murmurs are surprisingly common in dogs. According to the Merck Veterinary Manual, murmurs are detected in roughly 3.5% of all dogs presented to general veterinary practices, and the prevalence climbs sharply with age — affecting an estimated 10-15% of dogs over the age of nine. Some murmurs are "innocent" (also called physiologic or functional), particularly in puppies, and resolve on their own. Others signal structural heart disease that requires ongoing management.

Understanding the grading system, recognizing symptoms early, and knowing what diagnostic steps to expect will help you partner effectively with your veterinarian to protect your dog's heart health. Always consult your veterinarian for diagnosis and treatment planning — this guide is educational, not a substitute for professional veterinary care.

Understanding Dog Heart Murmurs: Grades and Classifications

Veterinarians classify heart murmurs on a standardized scale from Grade I to Grade VI based on their loudness and characteristics. This grading system, originally developed by Dr. Samuel Levine in 1933, remains the universal standard used in veterinary cardiology today.

It's important to understand that murmur grade does not always correlate perfectly with disease severity. A dog with a Grade III murmur could have more significant underlying heart disease than one with a Grade IV murmur. Your veterinarian will use the grade as one piece of a larger diagnostic picture, alongside imaging, bloodwork, and clinical signs.

Murmurs are also classified by timing within the cardiac cycle:

• Systolic murmurs — occur between the "lub" and "dub" heart sounds (most common; associated with mitral valve disease, subaortic stenosis)
• Diastolic murmurs — occur after the "dub" (less common; associated with aortic insufficiency)
• Continuous murmurs — heard throughout the entire cardiac cycle (classic sign of patent ductus arteriosus, or PDA)

Symptoms of a Heart Murmur in Dogs: Early Warnings vs. Advanced Signs

Many dogs with low-grade heart murmurs show zero outward symptoms. The murmur is often discovered incidentally during a wellness exam. As the underlying condition progresses, however, clinical signs begin to emerge. Recognizing the progression can mean the difference between early intervention and emergency crisis management.

Which Dog Breeds Are Prone to Heart Murmurs?

While any dog can develop a heart murmur, certain breeds carry significantly higher genetic risk for specific cardiac conditions that produce murmurs. Predisposition varies by the type of underlying heart disease:

How Veterinarians Diagnose the Cause of a Dog Heart Murmur

When your veterinarian detects a murmur, the next step is determining why it's there. The diagnostic process typically follows a tiered approach, starting with non-invasive screening and escalating to specialized cardiac evaluation as needed.

Step 1: Physical Examination & Auscultation

Your vet will listen carefully to the heart with a stethoscope, noting the murmur's grade, timing (systolic vs. diastolic), location on the chest, and whether it radiates. They'll also check gum color, femoral pulse quality, and lung sounds. Typical cost: $50-$90 (part of a standard exam fee).

Step 2: Thoracic Radiographs (Chest X-Rays)

X-rays reveal the heart's overall size and shape, and whether fluid is accumulating in or around the lungs — a hallmark of congestive heart failure. Three views (right lateral, left lateral, and ventrodorsal) are standard. Typical cost: $200-$450.

Step 3: Echocardiogram (Cardiac Ultrasound)

This is the gold standard for diagnosing the specific cause of a heart murmur. An echocardiogram allows the veterinarian (or veterinary cardiologist) to visualize the heart chambers, measure wall thickness, assess valve function, and quantify blood flow abnormalities using Doppler technology. Typical cost: $400-$800 at a general practice; $600-$1,200 with a board-certified veterinary cardiologist.

Step 4: Additional Diagnostic Tests

• Electrocardiogram (ECG/EKG): Measures the heart's electrical activity; identifies arrhythmias. Cost: $100-$300.
• Bloodwork (CBC, chemistry panel, NT-proBNP): The NT-proBNP test (cardiac biomarker) helps differentiate cardiac from respiratory causes of coughing. Cost: $80-$200 for standard panels; $150-$250 for NT-proBNP.
• Blood pressure measurement: Systemic hypertension can worsen cardiac disease. Cost: $40-$80.
• Heartworm antigen test: Rules out heartworm disease as a contributing factor. Cost: $35-$75.

Treatment Options for Dog Heart Murmurs

Because a heart murmur is a symptom rather than a disease, treatment targets the underlying cause. The approach depends entirely on what the echocardiogram and diagnostic workup reveal.

Commonly Prescribed Cardiac Medications

Your veterinarian will tailor the medication protocol to your dog's specific diagnosis and stage. Here are the most frequently used cardiac drugs:

• Pimobendan (Vetmedin): A positive inotrope and vasodilator — it strengthens heart contractions while reducing resistance. Dosed at 0.25-0.3 mg/kg every 12 hours. Given on an empty stomach (1 hour before food). Often the first medication started for MMVD and DCM. The EPIC study (2016) demonstrated pimobendan delays CHF onset in pre-clinical MMVD dogs with heart enlargement.
• Furosemide (Salix/Lasix): A loop diuretic that removes excess fluid from the lungs and body. Dosed at 1-4 mg/kg every 8-12 hours depending on severity. Dogs on furosemide need regular kidney function monitoring.
• Enalapril / Benazepril: ACE inhibitors that reduce blood pressure and cardiac workload. Dosed at 0.25-0.5 mg/kg every 12-24 hours. Bloodwork monitoring every 3-6 months is essential to track kidney values.
• Spironolactone: A potassium-sparing diuretic used as adjunct therapy. Dosed at 1-2 mg/kg every 12 hours. Shown to improve survival when combined with standard therapy in the DELAY study.
• Sotalol / Mexiletine: Anti-arrhythmic drugs used primarily in DCM patients with dangerous ventricular arrhythmias.

Prognosis and Life Expectancy for Dogs With Heart Murmurs

The prognosis for a dog with a heart murmur spans an enormous range — from a completely normal lifespan to a guarded outlook measured in months. The key variables are the underlying cause, the stage at diagnosis, and how well the dog responds to treatment.

The American College of Veterinary Internal Medicine (ACVIM) uses a staging system for myxomatous mitral valve disease that helps frame prognosis:

• Stage A: High-risk breed with no murmur or disease yet (e.g., a 3-year-old Cavalier). Monitoring only.
• Stage B1: Murmur present, but no heart enlargement on X-ray or echocardiogram. Monitoring every 6-12 months.
• Stage B2: Murmur with heart enlargement, but no CHF symptoms yet. This is when pimobendan treatment typically begins based on the EPIC trial criteria.
• Stage C: Current or past signs of congestive heart failure. Full medication protocol initiated.
• Stage D: End-stage CHF unresponsive to standard therapy. Requires specialized intervention.

Home Care and Daily Management

If your dog has been diagnosed with a heart condition causing a murmur, your daily management routine becomes a critical part of their treatment plan. Here's what life looks like at home:

Monitoring at Home

1. Resting respiratory rate (RRR): Count breaths per minute while your dog sleeps, ideally at the same time each day. Record the number in a log. Alert your vet if RRR consistently exceeds 30 breaths/minute or trends upward over several days.
2. Weight tracking: Weigh your dog weekly on the same scale. Sudden weight gain (fluid retention) or loss (cardiac cachexia) are both red flags.
3. Activity journal: Note any changes in exercise tolerance, coughing frequency, or reluctance to lie down.

Lifestyle Adjustments

• Exercise modification: Replace long, intense exercise with shorter, gentler walks. Multiple 10-15 minute walks are better than one 45-minute hike. Let your dog set the pace — if they stop or lag, respect it.
• Sodium restriction: Avoid high-sodium treats (jerky, deli meats, cheese). Prescription cardiac diets like Hill's h/d, Royal Canin Cardiac, or Purina Pro Plan Veterinary Diets NF are formulated with reduced sodium. Transition gradually over 7-10 days.
• Temperature control: Dogs with heart disease are more vulnerable to heat stress. Keep your home cool (below 75°F / 24°C), avoid midday walks in summer, and never leave your dog in a parked car.
• Stress reduction: Minimize stressful situations. Boarding, travel, and loud environments can increase cardiac demand. If boarding is unavoidable, inform the facility of your dog's condition and medications.
• Harness instead of collar: A harness distributes pressure across the chest rather than the neck, reducing vagal nerve stimulation that can affect heart rate.

Medication Administration Tips

• Give pimobendan on an empty stomach — 1 hour before or 2 hours after meals — for optimal absorption.
• Use a pill organizer labeled with days and times to avoid missed doses.
• Never double a missed dose. If you miss a dose by more than 4 hours, skip it and resume the normal schedule.
• Keep a medication log and bring it to every vet visit for dose reconciliation.

Cost of Heart Murmur Treatment in Dogs

The financial commitment for managing a dog with a heart murmur varies enormously depending on the underlying diagnosis, disease stage, and your geographic location. Here's a realistic breakdown based on 2026 veterinary pricing:

For families managing the cost of long-term cardiac care, consider these options:

• Pet insurance: If enrolled before diagnosis, most comprehensive plans cover 70-90% of cardiac care after deductible. Pre-existing conditions are excluded — which is why enrolling your dog while they're young and healthy is the best financial strategy.
• CareCredit / Scratchpay: Veterinary financing plans that offer 0% promotional periods for qualified applicants.
• Generic medications: Ask your vet about generic equivalents. Generic pimobendan, furosemide, and enalapril are significantly cheaper than brand-name versions and can be filled through pharmacies like Chewy Pharmacy, Costco, or Walmart.
• Veterinary teaching hospitals: University veterinary schools often offer cardiology consultations at lower rates than private specialty centers, while providing excellent care.

Prevention Strategies

Not all heart murmurs are preventable — congenital defects and genetically driven valve disease cannot be eliminated through lifestyle changes alone. However, you can significantly reduce risk factors and catch problems earlier:

• Annual wellness exams: For dogs under 7, yearly exams allow early murmur detection. For dogs over 7, twice-yearly exams are recommended by the AVMA.
• Heartworm prevention: Year-round heartworm preventive (e.g., Heartgard Plus, Interceptor Plus, Simparica Trio) is non-negotiable. Heartworm disease is entirely preventable but potentially fatal and expensive to treat. Cost: $60-$200/year depending on dog size.
• Weight management: Maintain your dog at an ideal body condition score (BCS) of 4-5 on a 9-point scale. Obesity increases cardiac workload and accelerates disease progression.
• Dental care: Advanced dental disease allows oral bacteria to enter the bloodstream, potentially seeding heart valve infections (endocarditis). Daily tooth brushing and professional cleanings under anesthesia reduce this risk.
• Breed-appropriate screening: If you own a high-risk breed, ask your vet about proactive cardiac screening. For Cavaliers, annual auscultation starting at age 2 is recommended. For Dobermans, annual Holter monitoring (24-hour ECG) and echocardiograms starting at age 3 can detect occult DCM before symptoms appear.
• Nutrition: Feed an AAFCO-complete diet. In 2018-2024, the FDA investigated a potential link between grain-free, legume-rich diets and DCM in non-traditional breeds. While the investigation remains inconclusive, many veterinary cardiologists recommend diets with AAFCO feeding trial testing from established manufacturers (Purina, Hill's, Royal Canin, Iams) for dogs at cardiac risk.

When to See the Vet: Emergency Red Flags

For non-emergency situations, schedule an appointment within 1-2 weeks if you notice:

• A new or changed cough that persists beyond a few days
• Gradual decrease in exercise tolerance
• A murmur was noted at a recent exam and follow-up diagnostics haven't been scheduled
• Your dog is on cardiac medications and you notice increased thirst, urination, or appetite changes

Frequently Asked Questions

What is a heart murmur in dogs?

A heart murmur is an abnormal whooshing or swishing sound heard through a stethoscope, caused by turbulent blood flow within the heart. It is a clinical sign, not a disease itself, and can indicate anything from an innocent flow variation to serious structural heart disease.

Can a dog heart murmur go away on its own?

Yes — "innocent" or physiologic murmurs in puppies commonly resolve by 4-6 months of age. These are typically Grade I-II and are not associated with any structural abnormality. In adult dogs, however, a new murmur rarely disappears without treatment of the underlying cause.

How much does it cost to treat a heart murmur in dogs?

Initial diagnosis typically costs $350-$2,500 depending on the tests performed and whether a specialist is involved. Monthly medication costs range from $40-$400 depending on disease stage. Emergency hospitalization for congestive heart failure can cost $1,500-$6,000 or more. First-year total expenses commonly fall between $1,200 and $8,000.

What is the life expectancy of a dog with a heart murmur?

Life expectancy ranges from a normal lifespan (innocent murmurs, surgically repaired PDA) to 6-18 months (dogs diagnosed with congestive heart failure from mitral valve disease). The prognosis depends entirely on the underlying cause, stage at diagnosis, and response to treatment.

Is a heart murmur painful for dogs?

The murmur itself is not painful. However, the underlying heart disease can cause discomfort as it progresses — fluid in the lungs causes breathlessness, and an enlarged heart can press on the airways, triggering coughing. Proper treatment significantly improves comfort and quality of life.

Should I restrict my dog's activity if they have a heart murmur?

Activity modification depends on the murmur grade and underlying diagnosis. Dogs with innocent murmurs or early-stage disease may not need any restrictions. Dogs with CHF should avoid strenuous exercise but benefit from gentle, short walks. Always follow your veterinarian's specific recommendations for your dog's condition.

Can diet affect a dog's heart murmur?

Diet plays a role in cardiac management. Sodium restriction helps reduce fluid retention in dogs with CHF. Some veterinary cardiologists recommend taurine and L-carnitine supplementation for certain breeds with DCM. Additionally, the FDA has investigated potential links between certain grain-free diets and DCM — discuss your dog's diet with your veterinarian, especially if they belong to a DCM-prone breed.