Symptoms, Diagnosis, Treatment & Prognosis Guide

When your veterinarian mentions a heart murmur during a routine exam, it's natural to feel alarm. But a heart murmur in dogs is not itself a disease — it's an abnormal sound caused by turbulent blood flow through the heart, detected via stethoscope. According to the Merck Veterinary Manual, murmurs are graded on a scale of I to VI based on loudness and are classified by timing (systolic, diastolic, or continuous). They affect an estimated 3–4% of the general dog population, with prevalence rising sharply in senior dogs and certain predisposed breeds. Some murmurs are innocent (physiologic) and require no treatment, while others signal underlying structural heart disease such as mitral valve disease, dilated cardiomyopathy, or congenital defects.

Understanding the type, grade, and cause of your dog's murmur is essential for making informed decisions about diagnostics, treatment, and long-term management. This guide breaks down everything you need to know — from early warning signs to real-world costs — so you can work confidently with your veterinary team.

What Is a Heart Murmur in Dogs?

A heart murmur is an extra or unusual sound heard between heartbeats, produced when blood flows turbulently through the heart chambers or valves. In a healthy dog, blood moves smoothly and quietly. When a valve is leaky, a chamber is enlarged, or a congenital defect creates an abnormal pathway, the resulting turbulence creates an audible vibration — the murmur.

Murmurs are categorized in three key ways:

• By timing: Systolic (during contraction), diastolic (during relaxation), or continuous (throughout the cardiac cycle).
• By grade: Grade I (barely audible) to Grade VI (so loud it can be felt through the chest wall). The American Kennel Club notes that grade does not always correlate with disease severity — a loud murmur can sometimes indicate a less dangerous condition than a soft one.
• By cause: Physiologic (innocent, often seen in puppies or anemic dogs), pathologic (structural heart disease), or extracardiac (caused by conditions outside the heart, such as fever, hyperthyroidism, or severe anemia).

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 incidentally during a wellness exam. When symptoms do appear, they typically reflect the underlying heart condition rather than the murmur itself. Here's what to watch for, organized by severity:

Risk Factors: Which Dogs Are Prone to Heart Murmurs?

How Veterinarians Diagnose the Cause of a Heart Murmur

Once a murmur is detected, your veterinarian will recommend a diagnostic workup to identify the underlying cause, assess severity, and establish a baseline. Here is the typical diagnostic process:

1. Physical examination & murmur grading — Your vet listens with a stethoscope, notes the murmur's grade (I–VI), timing, and location on the chest, and checks femoral pulse quality, gum color, and lung sounds. Cost: typically included in the exam fee ($50–$90).
2. Thoracic radiographs (chest X-rays) — Three-view chest X-rays reveal heart size (vertebral heart score), lung patterns (pulmonary edema or congestion), and airway compression. Cost: $200–$500 depending on clinic and whether sedation is needed.
3. Echocardiogram (cardiac ultrasound) — The gold standard for diagnosing the specific cause of a murmur. A veterinary cardiologist or trained general practitioner uses ultrasound to visualize valve structure, measure chamber dimensions, assess blood flow patterns (Doppler), and calculate fractional shortening (a measure of heart contractility). Cost: $400–$800 with a cardiologist; $300–$500 with a general practitioner.
4. Electrocardiogram (ECG/EKG) — Records the heart's electrical activity to detect arrhythmias such as atrial fibrillation or ventricular premature complexes. Cost: $75–$200.
5. Blood work & biomarkers — CBC, chemistry panel, and thyroid levels rule out extracardiac causes (anemia, hyperthyroidism). The NT-proBNP test (cardiopet, ~$100–$175) measures a biomarker released by stretched heart muscle and helps differentiate cardiac from respiratory causes of coughing. Total lab cost: $150–$350.
6. Blood pressure measurement — Systemic hypertension can worsen heart disease. Doppler or oscillometric blood pressure readings are quick and non-invasive. Cost: $30–$60.

Treatment Options for Dogs With Heart Murmurs

Treatment depends entirely on the underlying cause of the murmur, not the murmur itself. Innocent or physiologic murmurs (common in puppies) often resolve on their own by 6 months of age and require no treatment. Pathologic murmurs are managed based on the specific cardiac condition:

Important: Your veterinarian will determine appropriate medications and dosages based on your dog's weight, condition severity, and comorbidities. Never adjust cardiac medications without veterinary guidance. The AVMA recommends establishing a relationship with a board-certified veterinary cardiologist for complex cases.

Prognosis and Life Expectancy by Stage

The ACVIM (American College of Veterinary Internal Medicine) classifies canine heart disease into four stages. Prognosis depends heavily on the stage at diagnosis and the specific condition:

These are population-level estimates. Individual dogs may do significantly better or worse depending on the specific diagnosis, response to medication, and concurrent health conditions. Your veterinary cardiologist can provide a more personalized prognosis after a full cardiac evaluation.

Home Care and Daily Management

Once a cardiac diagnosis is established, your daily management routine becomes critical for maintaining quality of life and catching deterioration early:

Daily Monitoring

• Resting respiratory rate (RRR): Count breaths per minute while your dog is sleeping. Record the number in a log. A sustained increase above 30 breaths/minute or a sudden jump of 5+ breaths above your dog's personal baseline warrants a call to your vet.
• Weight tracking: Weigh your dog weekly on the same scale. Sudden weight gain (0.5–1 lb in 24–48 hours) can indicate fluid retention. Progressive weight loss may signal cardiac cachexia.
• Activity journal: Note any changes in walk duration tolerance, coughing frequency, or reluctance to lie down.

Lifestyle Adjustments

• Exercise: Moderate, consistent exercise is generally beneficial for dogs in Stages A–B2. Dogs in Stage C should have exercise restricted to short, gentle leash walks. Avoid intense play, heat exposure, and stressful situations.
• Diet: Feed a diet formulated for cardiac patients if recommended by your vet. Look for foods with controlled sodium levels, supplemented taurine, L-carnitine, and omega-3 fatty acids (EPA/DHA). Brands such as Royal Canin Veterinary Diet Cardiac and Hill's Prescription Diet h/d are commonly recommended. Avoid high-sodium treats (jerky, deli meats, cheese).
• Dental care: Periodontal disease increases the risk of bacterial endocarditis, which can worsen valve disease. Regular professional cleanings (under anesthesia with cardiac-safe protocols) and daily tooth brushing are important.
• Medication compliance: Cardiac medications must be given at exact intervals. Missing doses of diuretics can lead to rapid fluid buildup. Use pill organizers and phone alarms to maintain schedules.

Environmental Considerations

• Keep your home cool — dogs with heart disease are extremely heat-sensitive. Maintain indoor temperatures below 75°F (24°C).
• Use a harness instead of a collar to avoid tracheal pressure that can trigger coughing.
• Provide a ramp or steps for furniture access if your dog has exercise restrictions.

Cost of Heart Murmur Diagnosis and Treatment

Cardiac care costs vary widely based on your location, whether you see a general practitioner or a board-certified cardiologist, and the severity of disease. Here is a realistic cost breakdown:

Pet insurance can significantly offset these costs if enrolled before diagnosis. Most comprehensive plans cover cardiac diagnostics and medications, though pre-existing condition exclusions apply. If your dog is a breed predisposed to heart disease, enrolling in insurance during puppyhood is a financially prudent decision.

When to See the Vet Immediately

For non-emergency concerns — a new murmur detected at a routine visit, mild coughing, or slightly reduced exercise tolerance — schedule a standard appointment with your veterinarian within 1–2 weeks. Always consult your veterinarian before starting, stopping, or changing any medication.

Frequently Asked Questions About Heart Murmurs in Dogs

Can a heart murmur in dogs be cured?

Most heart murmurs caused by acquired valve disease or cardiomyopathy cannot be cured — they are managed long-term with medication. However, certain congenital defects like patent ductus arteriosus (PDA) can be effectively cured through surgical or catheter-based closure, giving the dog a near-normal lifespan. Innocent puppy murmurs typically resolve on their own by 4–6 months of age.

How long can a dog live with a heart murmur?

Life expectancy depends on the cause and stage. Dogs with low-grade innocent murmurs or early-stage (B1) mitral valve disease may live many years — often their full natural lifespan. Once congestive heart failure develops (Stage C), median survival with treatment is typically 9–12 months for MVD and 6–12 months for DCM, though some dogs exceed these averages significantly.

Is a heart murmur painful for dogs?

The murmur itself is not painful — it's simply a sound. However, the underlying heart disease can cause discomfort as it progresses: difficulty breathing is distressing, fluid accumulation creates pressure, and reduced cardiac output can cause weakness and exercise intolerance. Appropriate treatment significantly improves comfort and quality of life.

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

Activity restrictions depend on the stage of disease. Dogs in Stages A and B1 generally benefit from regular, moderate exercise. Dogs in Stage B2 should avoid intense exertion but can continue gentle walks. Dogs in Stage C (heart failure) require significant exercise restriction — short leash walks only, no running or rough play. Your veterinarian or cardiologist will provide specific guidance based on your dog's echocardiogram results.

What breeds are most prone to heart murmurs?

Small breeds are most commonly affected by mitral valve disease: Cavalier King Charles Spaniels, Miniature Poodles, Chihuahuas, Dachshunds, and Pomeranians top the list. Large breeds are more prone to dilated cardiomyopathy: Doberman Pinschers, Great Danes, Irish Wolfhounds, and Boxers. Congenital heart defects can occur in any breed but are overrepresented in German Shepherds (PDA), Boxers (subaortic stenosis), and Bulldogs (pulmonic stenosis).

Can diet affect my dog's heart murmur?

Diet plays an important supportive role. Low-sodium diets reduce fluid retention. Taurine and L-carnitine supplementation may help in DCM cases linked to nutritional deficiency (the FDA has investigated a potential link between grain-free boutique diets and DCM). Omega-3 fatty acids (fish oil) may help combat cardiac cachexia. Always discuss dietary changes with your veterinarian, especially if your dog is on cardiac medications.