What Is a Dog Heart Murmur? Symptoms, Grades, and Treatment Guide

Hearing your veterinarian say "your dog has a heart murmur" during a routine exam can feel alarming — but understanding what it actually means is the first step toward keeping your dog healthy. A heart murmur in dogs is an abnormal sound caused by turbulent blood flow through the heart, detected with a stethoscope during auscultation. It is not a disease itself but rather a clinical sign that may indicate an underlying cardiac condition, or in some cases, may be entirely benign.

Heart murmurs are surprisingly common. According to veterinary cardiology data published in the Journal of Veterinary Internal Medicine, approximately 3.5% to 7% of the general canine population has a detectable heart murmur at any given time, with prevalence rising sharply in older small-breed dogs — where rates can exceed 30% in dogs over 13 years of age. Puppies may also have "innocent" murmurs that resolve on their own by 6 months of age.

Murmurs are graded on a scale from I (barely audible) to VI (audible even without the stethoscope touching the chest). The grade helps your veterinarian determine urgency but does not always correlate directly with disease severity. Below, we break down everything you need to know — from early symptoms and diagnostic workups to realistic treatment costs and life expectancy.

What Is a Heart Murmur in Dogs?

A heart murmur is the sound of disrupted or turbulent blood flow within the heart chambers or through the heart valves. In a healthy canine heart, blood flows smoothly in one direction through four chambers separated by one-way valves. When a valve is leaky (regurgitation), narrowed (stenosis), or when there is an abnormal opening between chambers (septal defect), blood creates turbulence — and that turbulence produces the "whooshing" sound your vet hears.

Murmurs are classified in three ways:

• Timing: Systolic (during heart contraction — most common), diastolic (during relaxation), or continuous (throughout the cardiac cycle)
• Location: Left-sided or right-sided, and which valve area is loudest
• Grade: Intensity on the I–VI scale

Heart Murmur Grades Explained

Veterinarians use a standardized grading system to communicate murmur severity. Here is what each grade means in practical terms:

According to the Merck Veterinary Manual, murmur grade alone does not predict clinical outcome — a Grade II murmur from a congenital defect may require surgery, while a Grade IV murmur from myxomatous valve disease in a Cavalier King Charles Spaniel may be managed medically for years.

Symptoms of Heart Murmurs in Dogs

Many dogs with low-grade murmurs show no outward symptoms at all. The murmur is discovered incidentally during an annual wellness exam. When symptoms do appear, they typically indicate that the underlying condition has progressed to the point where the heart can no longer compensate. Recognizing the progression is critical.

Breeds Prone to Heart Murmurs and Risk Factors

Certain breeds carry well-documented predispositions to the conditions that cause heart murmurs:

The American Kennel Club notes that responsible breeders screen for heritable cardiac conditions through OFA (Orthopedic Foundation for Animals) cardiac evaluations and, where available, genetic testing. If you are acquiring a puppy from a predisposed breed, ask for parental cardiac clearance documentation.

How Veterinarians Diagnose the Cause of a Heart Murmur

Detection begins with auscultation (listening with a stethoscope), but identifying the cause requires additional diagnostics. Here is the typical diagnostic pathway your veterinarian will follow:

1. Physical exam and auscultation — The vet grades the murmur, notes its location and timing, checks gum color, measures heart rate, and palpates femoral pulses. Cost: included in exam fee ($55–$95).
2. Thoracic radiographs (chest X-rays) — Two to three views to evaluate heart size (vertebral heart score), pulmonary vasculature, and lung fields for fluid. Cost: $200–$450 depending on number of views and whether sedation is needed.
3. Echocardiogram (cardiac ultrasound) — The gold standard for diagnosing the specific cause. A board-certified veterinary cardiologist measures chamber dimensions, valve morphology, blood flow velocity (Doppler), and calculates fractional shortening (contractility). Cost: $400–$750 at a specialty center; $300–$500 if your general practitioner has ultrasound training.
4. Electrocardiogram (ECG) — Records electrical activity to identify arrhythmias that may accompany structural disease. Cost: $75–$200.
5. Blood work (CBC, chemistry panel, NT-proBNP) — NT-proBNP is a cardiac biomarker that helps distinguish cardiac from respiratory causes of coughing. A CARDIOPET® proBNP test costs $120–$180. Standard blood panels run $100–$200.
6. Blood pressure measurement — Systemic hypertension can worsen murmurs and is a comorbidity to manage. Cost: $30–$60.

Total initial diagnostic workup typically ranges from $500 to $1,500 depending on whether a specialist is involved and which tests are required. Your veterinarian may stage the diagnostics — starting with X-rays and blood work, then referring for an echocardiogram if structural disease is confirmed.

Treatment Options for Dog Heart Murmurs

Treatment depends entirely on the underlying cause of the murmur, not the murmur itself. An innocent puppy murmur requires no treatment at all. A murmur from advanced mitral valve disease may require lifelong multi-drug therapy. Here is a comparison of the most common treatment pathways:

The ACVIM consensus guidelines (updated through 2025) established the staging system (B1, B2, C, D) that guides when to start medication. The landmark EPIC study demonstrated that starting pimobendan in Stage B2 MMVD dogs delayed the onset of heart failure by a median of 15 months and extended survival significantly. Always consult your veterinarian before starting or adjusting any cardiac medication.

Prognosis and Life Expectancy by Stage

Prognosis varies enormously depending on the underlying cause, the stage at diagnosis, and how well the dog responds to treatment. Here is a realistic breakdown based on published veterinary cardiology data:

It is important to understand that these are medians — half of dogs live longer, half live shorter. Individual prognosis depends on the dog's overall health, comorbidities (such as kidney disease, which complicates diuretic use), medication compliance, and response to therapy. Your veterinary cardiologist will give you the most accurate prognosis after a complete echocardiogram.

Home Care and Daily Management

If your dog has been diagnosed with a heart condition causing their murmur, daily management at home plays a significant role in maintaining quality of life and catching decompensation early.

Daily Monitoring Protocol

• Resting respiratory rate (RRR): Count breaths per minute while your dog sleeps. Record in a log or app (the Cardalis app, developed by veterinary cardiologists, is designed specifically for this). Alert your vet if RRR consistently exceeds 30 breaths/minute.
• Weight tracking: Weigh weekly on the same scale. Sudden weight gain (1–2 lb in a small dog over 2–3 days) may signal fluid retention. Weight loss may indicate cardiac cachexia.
• Exercise tolerance log: Note any changes in walk duration willingness, panting episodes, or coughing after activity.

Lifestyle Adjustments

• Diet: Feed a commercially prepared diet that meets AAFCO standards. For dogs in heart failure, a sodium-restricted therapeutic diet (such as Hill's h/d or Royal Canin Veterinary Diet Cardiac) may be recommended by your vet. Avoid high-sodium treats and table scraps.
• Exercise: Dogs in Stage B can typically exercise normally. Dogs in Stage C should have controlled, moderate activity — short leash walks rather than running at the dog park. Avoid exercising in extreme heat or humidity.
• Dental care: Periodontal disease is a comorbidity that can worsen cardiac conditions through systemic inflammation and bacteremia. Maintain regular dental cleanings as advised by your vet.
• Stress reduction: Minimize situations that cause excessive excitement or anxiety, which increase cardiac demand. Use positive reinforcement training and desensitization techniques for fear triggers rather than aversive methods.

Medication Compliance

Cardiac medications must be given on schedule. Missing doses of furosemide can lead to rapid fluid re-accumulation and respiratory distress within 12–24 hours. Set phone alarms, use pill organizers, and never adjust dosages without veterinary guidance. If you are having difficulty administering medications, ask your vet about compounding options (flavored chews, transdermal gels) — many compounding pharmacies can prepare cardiac medications in easier-to-give forms.

Cost Breakdown: Diagnosis, Treatment, and Ongoing Care

Budgeting for a dog with a heart murmur depends on what is causing it. Here are realistic cost ranges based on 2025–2026 veterinary pricing data across US metropolitan and suburban practices:

For a dog with MMVD progressing from Stage B2 through Stage C over several years, total lifetime cardiac care costs typically range from $3,000 to $8,000. Pet insurance with a chronic condition rider can significantly offset these costs if enrolled before diagnosis.

When to See the Vet Immediately

For non-emergency concerns — a newly detected murmur, a mild cough that has developed over weeks, or a gradual decrease in exercise tolerance — schedule a regular veterinary appointment within 1–2 weeks. Your vet will perform auscultation and may recommend the diagnostic workup described above.

Prevention Strategies

Not all heart murmurs can be prevented — congenital defects and genetic predispositions are present from birth or inherited. However, several strategies can reduce risk or delay onset of acquired conditions:

• Heartworm prevention: Year-round heartworm preventive medication (ivermectin-based, milbemycin, or moxidectin products) is essential in endemic areas. Heartworm disease is a preventable cause of cardiac murmurs and heart failure. Products like Heartgard Plus®, Interceptor Plus®, and Revolution Plus® are FDA-approved options — your vet will recommend the right product for your dog's weight and region.
• Nutrition: Feed a complete-and-balanced diet meeting AAFCO standards. Following the FDA's investigation into a potential link between grain-free boutique diets and DCM (particularly in breeds not typically predisposed), the FDA recommends consulting your vet about diet choices, particularly if your dog is on a grain-free, legume-rich, or exotic-protein diet.
• Weight management: Obesity forces the heart to work harder. Maintain your dog's body condition score (BCS) at 4–5 on the 9-point scale.
• Regular veterinary exams: Twice-yearly wellness exams for dogs over 7 years allow early murmur detection, often before symptoms develop — when intervention is most effective.
• Responsible breeding: If acquiring a puppy from a predisposed breed, choose a breeder who performs OFA cardiac evaluations and breed-specific genetic testing on parent dogs.

Frequently Asked Questions

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

Yes — many dogs live years with a heart murmur, especially if it is low-grade or detected early. Dogs with innocent murmurs or Stage B1 MMVD often have normal lifespans and activity levels. The key is regular monitoring so that if the condition progresses, treatment begins at the optimal time.

Is a heart murmur painful for dogs?

The murmur itself is not painful — it is simply a sound. However, advanced heart disease can cause discomfort from fluid accumulation, difficulty breathing, and fatigue. Proper medication management significantly improves comfort and quality of life in symptomatic dogs.

Can a heart murmur in a dog go away on its own?

Innocent puppy murmurs (Grade I–II in puppies under 6 months) frequently resolve as the puppy matures. In adult dogs, murmurs caused by structural heart disease do not resolve spontaneously. However, murmurs caused by anemia, fever, or hyperthyroidism (rare in dogs) may resolve when the underlying condition is treated.

How much does an echocardiogram cost for a dog?

A complete echocardiogram performed by a board-certified veterinary cardiologist typically costs $400–$750 in the United States as of 2025–2026. General practitioners with ultrasound training may charge $300–$500. The initial consultation fee with the cardiologist ($150–$250) is usually additional.

What should I feed a dog with a heart murmur?

Dogs in early stages (B1, B2) without heart failure can eat their regular AAFCO-complete diet. Once heart failure develops (Stage C), your vet may recommend a sodium-restricted therapeutic diet. Avoid high-sodium treats (jerky, deli meats, commercial training treats with added salt). Omega-3 fatty acid supplementation (fish oil at 30–40 mg/kg EPA+DHA daily) may benefit dogs in heart failure — discuss with your vet before starting.

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

It depends on the stage. Dogs in Stage B1 and B2 can generally exercise normally — in fact, moderate exercise helps maintain muscle mass and cardiovascular fitness. Dogs in Stage C (heart failure) should have controlled, moderate activity: short walks on leash, avoiding sprinting, extreme heat, and situations that cause extreme excitement. Always follow your veterinarian's specific recommendations.

This article is for informational purposes and does not replace professional veterinary advice. If your dog has been diagnosed with a heart murmur or is showing symptoms of cardiac disease, consult your veterinarian or a board-certified veterinary cardiologist for a personalized diagnostic and treatment plan.