Heart Murmurs in Dogs: Symptoms, Diagnosis, and Treatment Guide
Complete guide to heart murmurs in dogs: causes, symptoms by severity, diagnosis costs, treatment options, prognosis by stage, and when to see the vet.
Hearing your veterinarian say "your dog has a heart murmur" can feel alarming, but understanding what it means is the first step toward keeping your dog healthy. A heart murmur in dogs is an abnormal sound heard during a heartbeat, caused by turbulent blood flow within the heart or its major vessels. Rather than a disease itself, a murmur is a clinical sign that may point to an underlying structural heart problem, a systemic condition, or — in some cases — nothing serious at all.
Heart murmurs are surprisingly common. Studies estimate that roughly 3–5% of the general dog population has a detectable murmur at any given time, and the prevalence climbs sharply with age. Among senior small-breed dogs, the figure may exceed 30%, largely driven by degenerative mitral valve disease (DMVD). Murmurs are graded on a scale from I (barely audible) to VI (audible even with the stethoscope off the chest), and the grade does not always correlate with disease severity.
This guide walks you through everything you need to know — from early symptoms and diagnostic workups to treatment costs and long-term prognosis — so you can partner effectively with your veterinarian.
What Causes Heart Murmurs in Dogs?
Heart murmurs arise when blood flow through the heart becomes turbulent. The underlying causes fall into two broad categories:
Innocent (Physiologic) Murmurs
Some murmurs are not linked to heart disease. These are common in puppies (often called "puppy murmurs") and typically resolve by 6 months of age. They are usually Grade I–II and heard best over the left heart base. High-output states such as anemia, fever, hyperthyroidism, or pregnancy can also produce innocent murmurs in adult dogs.
Pathologic (Disease-Related) Murmurs
These murmurs signal structural or functional heart problems:
- Degenerative Mitral Valve Disease (DMVD): The most common acquired heart disease in dogs, accounting for roughly 75% of canine cardiac cases. The mitral valve leaflets thicken and become nodular, allowing blood to leak backward into the left atrium.
- Dilated Cardiomyopathy (DCM): The heart muscle weakens and the chambers enlarge, reducing pumping efficiency. More common in large and giant breeds.
- Congenital Defects: Patent ductus arteriosus (PDA), pulmonic stenosis, subaortic stenosis (SAS), and ventricular septal defects (VSD) are present from birth.
- Heartworm Disease: Adult worms in the pulmonary arteries create turbulence and can cause a murmur alongside severe cardiopulmonary damage.
- Infective Endocarditis: Bacterial infection of the heart valves, though uncommon, produces a characteristic new or changing murmur.
Recognizing the Symptoms: Early Warning Signs vs. Advanced Disease
Many dogs with low-grade murmurs show no outward symptoms. The murmur is often first detected during a routine wellness exam. As heart disease progresses, however, clinical signs emerge. Use this checklist to understand what to watch for.
| Severity | Symptoms | What It Means |
|---|---|---|
| Early / Mild | Asymptomatic — murmur detected on exam only Slightly reduced exercise tolerance Occasional cough, especially at night or after excitement |
Heart is compensating; disease may be in ACVIM Stage B1 or B2 |
| Moderate | Persistent cough (dry, hacking, or honking) Noticeable exercise intolerance or reluctance to play Rapid or labored breathing at rest (>30 breaths/min) Mild abdominal distension |
Heart enlargement progressing; possible early congestive heart failure (CHF) |
| Advanced / Severe | Fainting or collapse (syncope) Severe difficulty breathing, open-mouth breathing Blue-tinged gums (cyanosis) Pronounced abdominal swelling (ascites) Extreme lethargy, inability to lie down comfortably Weight loss with muscle wasting (cardiac cachexia) |
Active congestive heart failure; emergency intervention required |
Resting respiratory rate (RRR) monitoring tip: Count your dog's breaths per minute while they are sleeping or resting calmly. A normal RRR is under 30 breaths per minute. Consistently elevated readings above 30–35 breaths/min warrant a veterinary recheck. Many cardiologists recommend tracking RRR daily once a murmur has been diagnosed.
Which Breeds Are Prone to Heart Murmurs?
Breed Predisposition & Risk Factors
Small breeds most affected by DMVD:
- Cavalier King Charles Spaniel — up to 50% develop DMVD by age 5, and over 90% by age 10 (AKC)
- Dachshund, Miniature Poodle, Chihuahua, Pomeranian, Shih Tzu, Maltese, Cocker Spaniel
Large breeds most affected by DCM:
- Doberman Pinscher — occult DCM prevalence estimated at 40–60% in screened populations
- Great Dane, Irish Wolfhound, Newfoundland, Boxer, Saint Bernard, German Shepherd
Congenital defect predispositions:
- PDA: Pomeranian, Collie, Shetland Sheepdog, Bichon Frise
- Subaortic stenosis: Golden Retriever, Rottweiler, Newfoundland, Boxer
- Pulmonic stenosis: Bulldog, Boxer, Beagle, Samoyed
Other risk factors:
- Age: Risk increases significantly after age 7–8 for DMVD; congenital murmurs present from puppyhood
- Weight: Obesity increases cardiac workload and accelerates disease progression
- Heartworm status: Unprotected dogs in endemic areas face elevated risk
- Diet: FDA has investigated a possible link between certain grain-free diets (high in legumes/potatoes) and DCM — consult your vet about your dog's diet (FDA)
How Are Heart Murmurs in Dogs Diagnosed?
When your veterinarian detects a murmur, they will recommend a diagnostic workup to determine the underlying cause, grade the severity, and stage the disease. The Merck Veterinary Manual outlines the standard diagnostic pathway.
- Step 1 — Physical Exam & Auscultation ($0–$65): Your vet listens with a stethoscope, grades the murmur (I–VI), identifies the location (left vs. right, base vs. apex), and checks femoral pulse quality, gum color, and lung sounds. If this is a routine wellness visit, the exam fee may be $50–$85.
- Step 2 — Thoracic Radiographs / X-rays ($150–$400): Two to three views of the chest reveal heart size (vertebral heart score), lung patterns (pulmonary edema or normal air), and airway compression. This is usually the first imaging test recommended.
- Step 3 — Echocardiogram ($350–$800): The gold standard for diagnosing the cause of a murmur. A veterinary cardiologist uses ultrasound to visualize valve structure, measure chamber dimensions, assess blood flow with Doppler, and calculate fractional shortening. This test is essential for staging DMVD (ACVIM B1, B2, C, D) and DCM.
- Step 4 — Blood Work & Biomarkers ($80–$250): A complete blood count (CBC), chemistry panel, and thyroid check rule out systemic causes. An NT-proBNP cardiac biomarker test ($65–$120) helps differentiate cardiac from respiratory causes of coughing and indicates myocardial stretch severity.
- Step 5 — Electrocardiogram / ECG ($75–$200): Assesses heart rhythm and detects arrhythmias such as atrial fibrillation or ventricular premature complexes that may accompany structural disease.
- Step 6 — Blood Pressure Measurement ($30–$60): Systemic hypertension can worsen murmurs and is screened with a Doppler or oscillometric cuff.
Total initial diagnostic cost range: $300–$1,800+ depending on how many tests are needed and whether a board-certified veterinary cardiologist performs the echocardiogram. A referral cardiology consultation with echocardiogram typically runs $500–$900 in most US metropolitan areas as of 2025–2026.
Treatment Options for Heart Murmurs in Dogs
Treatment depends entirely on the underlying cause and disease stage. Not all murmurs require medication — innocent murmurs and early-stage (ACVIM Stage B1) DMVD may only need monitoring.
| Stage / Condition | Treatment Approach | Common Medications | Monthly Cost Estimate |
|---|---|---|---|
| Innocent / Puppy Murmur | No treatment; recheck at 6 months | None | $0 |
| ACVIM B1 (DMVD — no enlargement) | Monitor every 6–12 months; no medication | None | $0–$50 (recheck exams) |
| ACVIM B2 (DMVD — heart enlargement) | Start pimobendan; monitor every 3–6 months | Pimobendan (Vetmedin) 0.25–0.3 mg/kg BID | $40–$120 |
| ACVIM C (CHF — first episode) | Multi-drug therapy; possible hospitalization | Pimobendan + Furosemide + ACE inhibitor (Enalapril/Benazepril) ± Spironolactone | $80–$250 |
| ACVIM D (Refractory CHF) | Escalated diuretics; additional agents; frequent rechecks | All above + Torsemide, Sildenafil (if pulmonary hypertension), Digoxin | $200–$500+ |
| DCM | Pimobendan, diuretics, ACE inhibitors, antiarrhythmics | Pimobendan + Furosemide + Enalapril ± Sotalol/Mexiletine | $100–$350 |
| Congenital (PDA, SAS, PS) | Surgical or interventional correction when possible | Pre/post-op medications; some require lifelong cardiac meds | Surgery: $3,500–$8,000 one-time |
| Heartworm Disease | Adulticide protocol (melarsomine injections) with strict rest | Doxycycline, prednisone, melarsomine, macrocyclic lactone preventive | $500–$1,500 total treatment |
Supportive Therapies
- Therapeutic diets: Prescription cardiac diets (e.g., Hill's h/d, Royal Canin Cardiac, Purina Pro Plan Veterinary Supplements CardioCare) are formulated with controlled sodium, supplemented taurine, L-carnitine, and omega-3 fatty acids. Expect $45–$90 per 12 lb bag.
- Supplements: Omega-3 fish oil (EPA/DHA at 30–40 mg/kg combined daily) has evidence for reducing cardiac cachexia. Coenzyme Q10 (1–2 mg/kg/day) is sometimes recommended, though evidence is limited. Always discuss supplements with your vet before adding them.
- Oxygen therapy: For dogs in acute CHF crisis, veterinary hospitalization with oxygen cage or flow-by oxygen is critical. Home oxygen concentrators can be rented for refractory cases ($150–$300/month).
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 what the veterinary literature tells us:
| Condition / Stage | Median Survival Time | Key Prognostic Factors |
|---|---|---|
| DMVD Stage B1 | Often normal lifespan — many dogs never progress | Murmur grade, rate of progression on serial echocardiograms |
| DMVD Stage B2 | Approximately 2–4 years with pimobendan (QUEST and EPIC study data) | Left atrial size, NT-proBNP levels, response to pimobendan |
| DMVD Stage C (first CHF episode) | Approximately 9–12 months median; some dogs live 2+ years with good management | Response to diuretics, owner compliance with RRR monitoring, renal function |
| DMVD Stage D (refractory CHF) | Weeks to a few months | Escalating diuretic requirements, worsening kidney values, quality of life |
| DCM (Doberman) | 3–6 months after CHF onset; occult stage may last years | Arrhythmia burden, presence of syncope, response to pimobendan |
| DCM (non-Doberman) | 6–24 months after CHF onset depending on breed and diet-related vs. genetic | Diet-related DCM may partially reverse with diet correction and taurine supplementation |
| PDA (surgically corrected) | Normal life expectancy if corrected before heart failure develops | Age at correction, residual shunting, pulmonary hypertension |
| PDA (uncorrected) | Many die of CHF within 1–2 years without intervention | Shunt size, development of Eisenmenger physiology |
It is important to understand that these are median values from published studies. Individual outcomes vary widely — some dogs exceed expectations significantly, especially with early diagnosis, consistent medication, and attentive home monitoring.
Home Care and Daily Management
If your dog has been diagnosed with a pathologic heart murmur, your daily role is critical. Here is what effective home management looks like:
Resting Respiratory Rate (RRR) Monitoring
This is the single most valuable thing you can do at home. While your dog is sleeping or resting calmly, count the number of breaths (one rise and fall of the chest = one breath) over 60 seconds, or count for 15 seconds and multiply by 4.
- Normal: Under 30 breaths per minute (most healthy dogs are 15–25)
- Caution: 30–40 breaths/min consistently — contact your vet within 24–48 hours
- Emergency: Over 40 breaths/min, or labored/open-mouth breathing — go to emergency vet immediately
Log RRR daily in a notebook or app (such as the "Your Dog's Heart" app or a simple spreadsheet). Bring this log to every vet appointment.
Exercise Modifications
- Stage B1–B2: Normal activity is usually fine. Avoid extreme exertion in hot/humid weather. Let your dog self-regulate — if they stop and rest, respect that.
- Stage C: Short, gentle leash walks (10–20 minutes, 1–2 times daily). Avoid stairs when possible. No rough play or sprinting.
- Stage D: Minimal exertion. Short potty breaks on-leash only. Carry small dogs up stairs.
Diet and Nutrition
- Feed a veterinary-recommended cardiac diet or a high-quality AAFCO-complete diet with moderate sodium restriction (your vet will advise on sodium levels).
- Maintain ideal body condition score (BCS 4–5/9). Both obesity and cardiac cachexia worsen outcomes.
- Avoid high-sodium treats: commercial jerky, cheese, deli meats, and most table scraps.
- Ensure adequate water intake — never restrict water even if your dog is on diuretics, unless specifically directed by your vet.
Medication Management
- Administer medications at consistent times. Pimobendan should be given on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption.
- Never stop cardiac medications abruptly without veterinary guidance — this can precipitate acute heart failure.
- Keep a medication log and set phone alarms. Missing doses of furosemide can lead to fluid buildup within 24–48 hours.
Understanding the Costs: Budgeting for Your Dog's Cardiac Care
Cardiac care is a long-term financial commitment. Here is a realistic breakdown based on 2025–2026 US veterinary pricing:
| Expense Category | Low Estimate | High Estimate | Frequency |
|---|---|---|---|
| Initial diagnostic workup (exam, X-rays, echo, blood work) | $500 | $1,800 | One-time |
| Cardiology referral consultation + echocardiogram | $450 | $900 | Annually or biannually |
| Monthly medications (pimobendan + diuretic + ACE inhibitor) | $80/mo | $350/mo | Ongoing |
| Recheck exams with X-rays and blood work | $200 | $450 | Every 3–6 months |
| Emergency CHF crisis (hospitalization, oxygen, IV diuretics) | $1,500 | $5,000+ | As needed |
| Congenital defect surgery (PDA occlusion, balloon valvuloplasty) | $3,500 | $8,000 | One-time |
| Estimated first-year total (Stage B2–C DMVD) | $2,500 | $7,000+ | Year 1 |
Pet insurance note: Most comprehensive pet insurance policies cover cardiac disease if it is not a pre-existing condition. Policies from providers such as Trupanion, Healthy Paws, and Nationwide typically reimburse 70–90% of eligible costs after deductible. If your dog has not yet been diagnosed, enrolling early is financially prudent — annual premiums for a mid-size dog range from $400–$900/year depending on age, breed, and location.
Prevention Strategies
Not all heart murmurs can be prevented — congenital defects and genetically driven DMVD/DCM are not avoidable through lifestyle alone. However, you can reduce risk and slow progression:
- Heartworm prevention: Year-round monthly heartworm preventive (ivermectin-based products like Heartgard Plus, or milbemycin-based like Interceptor Plus) costs $60–$150/year and virtually eliminates heartworm-associated murmurs. The American Heartworm Society recommends year-round prevention regardless of geography.
- Weight management: Keeping your dog at ideal BCS (4–5/9) reduces cardiac workload. Studies show obese dogs have higher rates of cardiovascular compromise.
- Diet quality: Feed an AAFCO-tested, complete-and-balanced diet. If your dog is a breed predisposed to DCM, discuss diet with your vet — the FDA's investigation into grain-free diets and DCM suggests choosing diets from manufacturers with robust feeding trials and veterinary nutritionist oversight (e.g., Purina, Hill's, Royal Canin, Iams).
- Regular wellness exams: Annual exams (twice yearly for seniors) allow early murmur detection. A murmur caught at Stage B1 allows monitoring; caught at Stage B2, pimobendan can delay CHF onset by approximately 15 months (per the EPIC study published in the Journal of Veterinary Internal Medicine).
- Dental care: While the direct causal link between periodontal disease and endocarditis in dogs is debated, severe dental disease introduces bacteria into the bloodstream. Professional dental cleanings under anesthesia and daily tooth brushing support overall cardiovascular health.
- Responsible breeding: If you are selecting a puppy from a breed predisposed to cardiac disease, ask the breeder for proof of cardiac screening (OFA/Cardiac or breed-specific clearances). For Cavaliers, a cardiologist evaluation of both parents is strongly recommended.
🚨 When to See the Vet Immediately
Go to your nearest emergency veterinary hospital if your dog shows any of these red-flag symptoms:
- Open-mouth breathing or panting while at rest — dogs should breathe through their nose at rest
- Respiratory rate over 40 breaths/min while sleeping
- Blue, gray, or white gums (cyanosis) — indicates critically low blood oxygen
- Fainting or collapse — even brief episodes signal serious cardiac compromise
- Extreme restlessness, inability to lie down or get comfortable — often indicates pulmonary edema
- Coughing up pink, frothy fluid — hallmark of acute pulmonary edema
- Sudden, severe abdominal swelling — may indicate right-sided heart failure with ascites
- Known heart murmur dog with sudden weakness or hind limb coldness/paralysis — could indicate aortic thromboembolism (rare in dogs but possible)
Do not wait for a scheduled appointment. Acute CHF can be fatal within hours without oxygen and IV diuretics.
Frequently Asked Questions
What is a heart murmur in dogs?
A heart murmur is an abnormal swishing or whooshing sound heard between normal heartbeats, caused by turbulent blood flow. It is not a disease itself but a sign that may indicate valve disease, heart muscle disease, a congenital defect, anemia, or other conditions. Murmurs are graded I through VI based on loudness and character.
Can a heart murmur in dogs be cured?
It depends on the cause. Innocent puppy murmurs often resolve on their own. Congenital defects like PDA can be surgically corrected with excellent outcomes. However, the most common causes — DMVD and DCM — are progressive and cannot be cured, but they can be managed with medication to extend quality life for months to years. Heartworm-associated murmurs may resolve after successful adulticide treatment if permanent damage has not occurred.
How much does heart murmur treatment cost?
Initial diagnosis ranges from $500–$1,800. Ongoing monthly medication costs typically fall between $80–$350 depending on disease stage and dog size. Emergency CHF hospitalization can cost $1,500–$5,000+. Congenital defect surgery ranges from $3,500–$8,000. First-year total costs for a dog with Stage B2–C DMVD typically run $2,500–$7,000+.
What is the life expectancy of a dog with a heart murmur?
Life expectancy depends entirely on the underlying cause and stage. Dogs with innocent murmurs or Stage B1 DMVD often live a normal lifespan. Dogs with Stage B2 DMVD on pimobendan average 2–4 years before CHF onset. Once CHF develops (Stage C), median survival is approximately 9–12 months, though some dogs live 2+ years. DCM prognosis is generally shorter, especially in Dobermans (3–6 months after CHF onset).
Which breeds are most prone to heart murmurs?
Small breeds most affected include Cavalier King Charles Spaniels (up to 90% by age 10), Dachshunds, Miniature Poodles, Chihuahuas, and Pomeranians — primarily from DMVD. Large breeds prone to DCM include Doberman Pinschers, Great Danes, Irish Wolfhounds, and Boxers. Congenital defects cluster in specific breeds: PDA in Pomeranians and Collies, subaortic stenosis in Golden Retrievers and Rottweilers.
Should I restrict my dog's activity if they have a heart murmur?
For early-stage disease (B1–B2), moderate exercise is generally fine and beneficial for maintaining fitness and healthy weight. Let your dog self-regulate — if they slow down or stop, do not push them. For dogs in CHF (Stage C–D), limit activity to gentle leash walks and avoid heat, humidity, and excitement that triggers heavy panting. Your veterinarian or cardiologist will give you specific exercise guidance based on your dog's echocardiogram results.
Can diet affect heart murmurs in dogs?
Diet can play a significant role. The FDA has investigated links between certain grain-free, legume-rich diets and DCM — some dogs showed improvement after diet change and taurine supplementation. For dogs in heart failure, veterinary cardiac diets with controlled sodium and supplemented nutrients (taurine, carnitine, omega-3s) support management. Always discuss diet changes with your veterinarian, and avoid high-sodium treats and human foods.
Heart murmurs in dogs range from benign findings that need only periodic monitoring to signs of serious progressive disease. The key is early detection, accurate diagnosis by a qualified veterinary team, and consistent home management. By monitoring your dog's resting respiratory rate, keeping up with recheck appointments, and administering medications faithfully, you give your dog the best possible chance at a long, comfortable life.
Tom Renshaw
All our authors care for dogs every day — read more of their work on the authors page.
