Heart Murmur in Dogs: Symptoms, Grades, Diagnosis & Treatment Guide

Hearing your veterinarian say "your dog has a heart murmur" can feel alarming — but not all murmurs are created equal. A heart murmur in dogs is an abnormal sound heard during a heartbeat, caused by turbulent blood flow within or near the heart. Rather than a disease itself, a murmur is a clinical sign that may point to an underlying cardiac condition, or in some cases, may be completely benign. According to the Merck Veterinary Manual, heart murmurs are among the most common cardiac findings in dogs, with prevalence estimates ranging from 3.5% to over 15% depending on the population studied and the dog's age. Small breeds are disproportionately affected by degenerative valve disease, while large breeds are more prone to cardiomyopathies that can produce murmurs.

Understanding the grading system, the diagnostic workup your vet will recommend, and the realistic outcomes for each severity level will help you make informed decisions about your dog's cardiac care. This guide walks you through everything a dog owner needs to know — from the moment a murmur is first detected through long-term management.

What Is a Heart Murmur in Dogs?

A heart murmur is the sound of blood flowing turbulently through the heart chambers or great vessels. A normal heartbeat produces two distinct sounds — "lub-dub" — corresponding to the closure of the heart valves. When blood leaks backward through a valve that doesn't close fully (regurgitation), pushes through a narrowed opening (stenosis), or flows through an abnormal passage (such as a septal defect), the resulting turbulence creates a swishing or whooshing sound your veterinarian detects with a stethoscope.

Heart murmurs in dogs are classified into two broad categories:

• Physiologic (innocent) murmurs: Common in puppies under 6 months of age, these murmurs are not associated with structural heart disease and typically resolve on their own as the cardiovascular system matures. They may also appear in dogs with anemia, fever, or hyperthyroidism.
• Pathologic murmurs: These indicate underlying cardiac disease — such as myxomatous mitral valve disease (MMVD), dilated cardiomyopathy (DCM), patent ductus arteriosus (PDA), or aortic stenosis — and require further investigation and often treatment.

Murmurs are graded on a standardized scale from I to VI based on their loudness and the presence of a palpable vibration (called a "thrill") on the chest wall:

Grade	Description	Clinical Significance
I	Very soft, heard only in a quiet room after careful listening	Often innocent in puppies; may warrant monitoring in adults
II	Soft but readily audible	Common with early valve disease
III	Moderately loud, no thrill	Usually pathologic; warrants diagnostic workup
IV	Loud, no thrill	Typically indicates significant structural disease
V	Very loud with palpable thrill on chest wall	Advanced disease likely
VI	Extremely loud with thrill, audible with stethoscope partially off chest	Severe cardiac pathology

Important caveat: Murmur grade does not always correlate perfectly with disease severity. A Grade II murmur from a small PDA can be more hemodynamically significant than a Grade IV murmur from mild mitral regurgitation. Your veterinarian will use the grade as one data point among many.

Symptoms of Heart Murmurs in Dogs: Early Warning Signs vs. Advanced Disease

Many dogs with low-grade murmurs show no outward symptoms at all — the murmur is discovered during a routine wellness exam. As the underlying condition progresses, clinical signs emerge as the heart's pumping efficiency declines. The American Kennel Club notes that symptom onset can be gradual, making it easy to attribute early changes to aging rather than cardiac disease.

Which Breeds Are Prone to Heart Murmurs?

While any dog can develop a heart murmur, certain breeds carry significantly higher genetic risk for the cardiac conditions that produce them. The predisposition splits largely along size lines:

How Veterinarians Diagnose the Cause of a Heart Murmur

When your vet detects a murmur, the next step is determining whether it's innocent or pathologic — and if pathologic, identifying the specific underlying condition and its stage. This typically involves a staged diagnostic approach, with tests escalating based on initial findings.

In many cases, the echocardiogram provides the definitive diagnosis. For congenital defects like PDA, the echocardiogram can also determine whether the defect is surgically correctable. If your general practitioner is uncertain about the murmur's origin, referral to a board-certified veterinary cardiologist (DACVIM-Cardiology) is strongly recommended before initiating long-term medications.

Treatment Options: Medical, Surgical, and Supportive Care

Treatment depends entirely on the underlying cause and the stage of disease. An innocent puppy murmur requires no treatment. A Grade III murmur from early-stage MMVD may only need monitoring. Advanced heart failure requires multi-drug therapy and sometimes hospitalization.

A note on supplements: Omega-3 fatty acids (EPA and DHA) at doses of approximately 30 mg combined EPA+DHA per kg of body weight daily have shown modest benefits in reducing cardiac cachexia and inflammation in dogs with heart failure, according to research from the Cummings School of Veterinary Medicine at Tufts University. Coenzyme Q10 and taurine may benefit specific conditions (taurine-responsive DCM in Cocker Spaniels), but should only be added under veterinary guidance.

Prognosis and Life Expectancy by Stage and Severity

Prognosis varies dramatically based on the underlying cause, the stage at diagnosis, and the dog's response to treatment. The following table summarizes expected outcomes based on published veterinary cardiology data:

It's important to understand that these are population medians — individual dogs may do significantly better or worse. Some dogs with Stage C MMVD live over two years on optimized therapy, while others decline rapidly. Your veterinary cardiologist can provide a more personalized prognosis after reviewing your dog's echocardiogram measurements.

Home Care and Daily Management for Dogs With Heart Murmurs

If your dog has been diagnosed with a pathologic heart murmur and is on treatment, consistent home management directly impacts quality of life and survival time.

Monitor Resting Respiratory Rate (RRR)

This is the single most useful at-home monitoring tool for dogs with heart disease. Count your dog's breaths per minute while they are sleeping or resting quietly. One breath equals one inhale plus one exhale (watch the chest rise and fall). Normal sleeping RRR is 15–30 breaths per minute. If your dog's sleeping RRR consistently exceeds 30–35, or trends upward over several days, contact your veterinarian — this often precedes visible signs of fluid buildup by 24–72 hours.

Medication Adherence

Cardiac medications must be given on a strict schedule. Missing even one or two doses of furosemide can allow fluid to re-accumulate in the lungs. Set phone alarms, use a pill organizer, and keep a written log of administration times. Never double a missed dose without veterinary guidance.

Dietary Management

• Sodium restriction: Dogs in heart failure benefit from moderate sodium restriction. Prescription cardiac diets (Hill's h/d, Royal Canin Cardiac, Purina Pro Plan Veterinary Diets NC) are formulated for this purpose. Avoid high-sodium treats like jerky, cheese, and deli meats.
• Caloric adequacy: Cardiac cachexia (muscle wasting) is common in advanced disease. If your dog is losing weight despite eating, discuss appetite stimulants (such as capromorelin/Entyce®) or feeding tube options with your vet.
• Grain-free diet caution: If your dog has been diagnosed with DCM and is eating a grain-free, legume-rich, or boutique diet, discuss transitioning to a WSAVA-compliant diet with your veterinarian. The FDA's ongoing investigation into diet-associated DCM recommends consulting your vet about diet choices.

Exercise and Lifestyle

Dogs with early-stage disease should continue regular, moderate exercise — short leash walks, gentle play. Avoid strenuous activity that causes heavy panting or collapse. Dogs in heart failure may need restricted activity. Keep your dog at an ideal body condition score (BCS 4–5 on a 9-point scale) — excess weight increases cardiac workload. In hot or humid weather, limit outdoor time and ensure access to air conditioning.

Stress Reduction

Minimize stressful situations. Excitement increases heart rate and oxygen demand. If your dog becomes overly stimulated by visitors, create a quiet retreat space. Use positive reinforcement training to teach calm settling behaviors — never use aversive tools like shock or prong collars, which spike stress hormones and heart rate.

How Much Does Heart Murmur Diagnosis and Treatment Cost?

Cardiac care costs vary significantly by region, facility type (general practice vs. specialty), and disease severity. Here's a realistic breakdown based on 2025–2026 pricing from US veterinary practices:

Expense Category	Estimated Cost Range	Frequency
Initial exam with murmur detection	$55–$120	One-time (or annual wellness)
Chest radiographs (2 views)	$200–$450	At diagnosis; then every 6–12 months
Echocardiogram (general practice)	$400–$800	At diagnosis; then annually or as recommended
Echocardiogram (cardiology specialist)	$600–$1,200	Same as above
ECG	$75–$200	At diagnosis; as needed
Holter monitor (24-hour)	$300–$600	As needed for arrhythmia evaluation
Blood work (CBC + chemistry + NT-proBNP)	$200–$450	At diagnosis; then every 3–6 months on medications
Pimobendan (Vetmedin®) monthly	$40–$120/month	Ongoing (dose-dependent)
Furosemide monthly	$10–$30/month	Ongoing
ACE inhibitor (enalapril/benazepril) monthly	$15–$40/month	Ongoing
Spironolactone monthly	$15–$35/month	Ongoing
PDA closure (interventional/surgical)	$3,500–$7,000	One-time
Emergency hospitalization for acute heart failure	$1,500–$5,000+	As needed
First-year total (diagnosis + medications, MMVD Stage B2–C)	$1,200–$3,500	—
Ongoing annual cost (monitoring + medications)	$800–$2,500	—

Cost management tips: Pet insurance purchased before diagnosis can cover a significant portion of cardiac care, though pre-existing conditions are universally excluded. If you don't have insurance, ask your vet about generic medication options (generic pimobendan is now available and costs 30–50% less than brand-name Vetmedin®). Many veterinary schools offer cardiology consultations at lower rates than private specialty centers. Organizations like the AVMA and local veterinary associations can help you find low-cost diagnostic resources.

Prevention Strategies: Reducing Risk Where Possible

Not all heart murmurs are preventable — genetic conditions like MMVD in Cavaliers or DCM in Dobermans are inherited. However, you can take meaningful steps to reduce risk and catch disease early:

• Annual wellness exams: Twice-yearly exams for dogs over age 7 allow early murmur detection before symptoms appear. Early-stage intervention with pimobendan (for MMVD Stage B2) significantly extends the pre-failure period.
• Heartworm prevention: Heartworm disease causes pulmonary hypertension and secondary murmurs. Year-round preventive medication (ivermectin, milbemycin, moxidectin, or selamectin-based products) is essential in all US regions.
• Weight management: Maintaining an ideal BCS reduces cardiac workload. Obesity is a modifiable risk factor that accelerates progression of existing heart disease.
• Dental care: Chronic periodontal disease introduces bacteria into the bloodstream, which can colonize damaged heart valves (bacterial endocarditis). Daily tooth brushing and professional dental cleanings reduce this risk.
• Diet quality: Feed diets that meet AAFCO nutritional adequacy standards and are formulated by companies employing full-time veterinary nutritionists. Discuss any grain-free or boutique diet choice with your vet, particularly for breeds predisposed to DCM.
• Responsible breeding: If you're acquiring a puppy from a predisposed breed, choose a breeder who performs cardiac screening — including echocardiograms and Holter monitoring — on breeding stock. The Cavalier King Charles Spaniel Club USA recommends cardiac evaluation by a veterinary cardiologist for all breeding Cavaliers.

Frequently Asked Questions About Heart Murmurs in Dogs

This guide is for educational purposes and does not replace professional veterinary advice. If your dog has been diagnosed with a heart murmur, consult your veterinarian or a board-certified veterinary cardiologist for individualized diagnosis and treatment planning. Always discuss medication changes, dietary modifications, and exercise plans with your veterinary team before implementation.