Updated on August 12, 2026
A heart murmur is an abnormal sound heard on auscultation, caused by turbulent blood flow inside the heart — in puppies, it’s often harmless and disappears before 4-5 months of age; in adult or senior dogs, it almost always signals an underlying structural heart condition and warrants further testing. The murmur’s grade (1 to 6) gives a first indication, but it never replaces an echocardiogram for assessing the actual severity. Here’s how to interpret a heart murmur based on your dog’s age, when to worry, and how to monitor a dog that’s already been diagnosed.
What is a heart murmur in dogs? #
A heart murmur is an abnormal sound heard through a stethoscope, between or during a dog’s normal heartbeats, caused by turbulent blood flow — most often because a heart valve no longer closes properly (it “leaks”), or because a malformation changes how blood moves through the heart. It’s not a disease on its own, but a clinical sign that should be traced back to a specific cause.
The 6 grades of heart murmurs in dogs (Levine scale) #
Vets classify a murmur’s intensity on a 1-to-6 scale, but this grade mainly measures how loud the sound is, not directly how severe the underlying condition is.
| Grade | Description |
|---|---|
| 1 | Extremely soft, barely audible even with a stethoscope |
| 2 | Soft but clear, easily heard with a stethoscope |
| 3 | Moderate intensity, heard at several points on the chest |
| 4 | Moderate to loud, audible on both sides of the chest |
| 5 | Very loud, audible even with the stethoscope barely touching the chest |
| 6 | The most intense, sometimes felt even without a stethoscope, by hand on the chest |
From grade 3 upward — or if the murmur is continuous, heard best on the right side, or worsening over time — a full cardiac work-up (echocardiogram) is recommended. The grade alone is never enough to assess the real severity of a valve disease.
Murmur in puppies vs. adult dogs: two very different situations #
The cause of a heart murmur depends almost entirely on the dog’s age when it’s first detected.
In puppies, a soft murmur is often an “innocent murmur,” linked to a still-maturing cardiovascular system: it usually disappears before 4 to 5 months of age, with no lasting consequence. But a murmur that persists past that age can point to a congenital malformation, the most common being patent ductus arteriosus (PDA), which particularly affects Maltese, Pomeranians, Poodles, Keeshonds, Bichons, and German Shepherds.
In adult or senior dogs, a murmur almost always reflects an acquired structural heart condition — most often mitral valve disease (MVD), involving a leaking mitral valve, or less commonly dilated cardiomyopathy (DCM). Roughly 10% of dogs of all ages, and up to 75% of senior dogs, have some detectable form of heart disease — which shows just how significant a murmur found during a routine check-up can be in an older dog.
Which breeds are most predisposed? #
| Context | Most affected breeds |
|---|---|
| Innocent puppy murmur | All breeds, usually disappears before 4-5 months |
| Patent ductus arteriosus (PDA) | Maltese, Pomeranian, Poodle, Keeshond, Bichon, German Shepherd |
| Mitral valve disease (adult/senior) | Cavalier King Charles, Boston Terrier, Chihuahua, Yorkshire, Dachshund, Poodle |
| Dilated cardiomyopathy (adult/senior) | Doberman, Boxer, Great Dane, Golden Retriever |
When should you worry about a heart murmur in your dog? #
A heart murmur calls for a full evaluation once it exceeds grade 2, is continuous, is heard best on the right side of the chest, persists past 6 months in a puppy, or comes with another sign: coughing, breathlessness, unusual fatigue, fainting. Conversely, a soft murmur (grade 1-2) in a puppy under 4-5 months, with no other symptom, is usually just monitored, with no urgency.
Diagnosis: what tests follow the discovery of a murmur? #
After auscultation, the most common follow-up tests are:
- a chest X-ray, to check the heart’s size;
- an echocardiogram, the gold-standard test to pinpoint the murmur’s cause and stage (see the ACVIM A-to-D classification);
- an electrocardiogram (ECG), if an arrhythmia is suspected alongside the murmur;
- blood tests, sometimes including cardiac biomarkers.
Heart murmur and congestive heart failure: what’s the connection? #
A heart murmur is not congestive heart failure, but it’s often its first warning sign, sometimes years before any symptom appears. In the ACVIM classification, a murmur with a still-normal-sized heart corresponds to stage B1; a murmur combined with an enlarged heart corresponds to stage B2 — the most strategic stage, since treatment started at that point significantly delays the onset of congestive heart failure.
How to monitor a dog with a heart murmur day to day #
Once a murmur is detected, home monitoring becomes a valuable complement between vet visits, particularly for catching a possible progression toward heart failure before it becomes symptomatic.
The Biotracker continuously measures your dog’s heart and respiratory rate, with an accuracy validated at 99.6% and 98.6% respectively against a portable ECG and manual counting, as part of the AI-COLLAR study conducted on 703 dogs across 29 countries. This continuous monitoring doesn’t replace auscultation or an echocardiogram — it doesn’t detect the murmur itself — but it lets you track, over time, the parameters that shift as the condition progresses, and share that data with your vet through a PDF report or the Biotrack platform, which sorts alerts by AI based on how far they deviate from your dog’s baseline values.
These digital cardiac biomarker research projects for dogs are developed with veterinary cardiologists, which sets this approach apart from a simple activity-tracking gadget.
FAQ #
Is a heart murmur in dogs always serious? #
No. In puppies, a soft murmur (grade 1-2) is often innocent and disappears before 4-5 months. In adults or seniors, a murmur generally reflects a structural heart condition, but its real severity depends on its cause and stage — not just its intensity — and should be assessed by echocardiogram.
Does the murmur’s grade indicate how severe the disease is? #
Not directly. The grade (1 to 6) measures how loud the murmur sounds, not how severe the underlying condition is. A faint murmur can correspond to already-advanced disease, and vice versa. It’s a clue that guides the exam, not a diagnosis in itself.
What’s the most common cause of heart murmurs in adult dogs? #
Degenerative mitral valve disease, which mainly affects small breeds such as the Cavalier King Charles Spaniel, Boston Terrier, or Dachshund from around 6-7 years old. It accounts for the vast majority of murmurs detected in adult and senior dogs.
My puppy has a heart murmur — should I be worried? #
Not necessarily. A soft murmur in a puppy under 4-5 months, with no other symptom, is often an innocent murmur that resolves on its own. That said, a murmur that persists past 5-6 months, or that’s louder than grade 2, warrants a check-up to rule out a congenital malformation like patent ductus arteriosus.
Can you monitor a heart murmur at home without a stethoscope? #
Yes, partly: you can’t hear the murmur itself without a stethoscope, but you can track at home the parameters that shift as the disease progresses — resting heart and respiratory rate, endurance, coughing. A device like the Biotracker automates this monitoring continuously between vet visits.
Can a heart murmur progress into congestive heart failure? #
Yes — that’s the most common progression for unmonitored mitral valve disease: the murmur marks the preclinical stages (B1, B2), before congestive heart failure itself sets in (stage C). It’s precisely during this silent phase that regular monitoring makes the biggest difference.
A heart murmur should be monitored, not ignored #
A heart murmur is neither a reason for automatic panic nor a detail to overlook: it’s a signal that deserves to be assessed based on your dog’s age, the murmur’s intensity, and how it evolves over time. Between regular vet check-ups and continuous heart and respiratory rate monitoring with the Biotracker, you give your dog — and their vet — the best chance of catching a change before it becomes symptomatic.