Is It Normal for a Puppy to Have a Heart Murmur?

Yes, it is reasonably common for a veterinarian to hear a murmur in a young puppy, and a large share of those murmurs turn out to be innocent sounds that fade as the puppy grows. Even so, any murmur found in a puppy should be examined by a veterinarian, because an identical sound can come from a congenital heart defect, and if your puppy is also collapsing, breathing hard at rest, or has pale or bluish gums, that is an emergency visit today, not a wait-and-see.

A murmur is not a diagnosis. It is a finding: an extra sound your vet hears through the stethoscope between or during the normal lub-dub. What matters next is why it is there, how loud it is, where on the chest it is loudest, how old your puppy was when it appeared, and whether your puppy is growing and playing normally. Those details are what separate a murmur that disappears on its own from one that needs a cardiologist.

What a murmur actually is, and why young dogs get them

Blood normally moves through the heart in smooth, quiet layers. A murmur is the sound of that flow becoming turbulent, either because it is moving faster than usual, because it is squeezing through a narrowed opening, or because it is leaking backward through a valve or a hole that should not be there.

In puppies, several harmless things speed blood up. A growing puppy has a high heart rate, a thin chest wall that transmits sound well, and a relatively large stroke volume for its body size. Excitement, fever, dehydration and anaemia all increase turbulence too, which is why a puppy carrying a heavy hookworm or flea burden can develop a murmur that resolves once the anaemia is corrected. These are called innocent, physiologic or flow murmurs. Research suggests that soft flow murmurs of this kind are common in healthy puppies and usually fade as the chest fills out and the resting heart rate slows, often by around four to six months of age.

The other category is congenital: a structural difference the puppy was born with. The ones veterinarians diagnose most often include patent ductus arteriosus (a fetal blood vessel that should close at birth and does not), pulmonic stenosis and subaortic stenosis (narrowing at a valve), ventricular septal defect (a hole between the pumping chambers) and malformed mitral or tricuspid valves. Some breeds carry more risk than others, which is one reason your vet will ask what your puppy is.

Innocent or congenital: how vets tell the difference

There are patterns that make a murmur more or less suspicious, but none of them is proof on its own.

Feature	More typical of an innocent murmur	More concerning for a defect
Loudness	Soft, grade I to II, rarely above III	Grade III or louder, or any thrill
Timing	Early in systole, short	Long, continuous, or machinery-like
Location	Left heart base, one small spot	Loud over a wide area or on the right side
Changes	Softer at rest, varies with position	Stable or getting louder over time
The puppy	Growing well, keeps up with littermates	Slow growth, tires early, coughing, fainting
Over time	Fades and disappears with age	Persists past five to six months

An innocent murmur and a serious congenital defect can sound alike through a stethoscope, which is why an echocardiogram, not the grade, is what finally tells you which one your puppy has.

What a puppy heart murmur sounds like, and what the grades mean

Most owners never hear it themselves. It takes a stethoscope on a quiet dog in a quiet room. Described in plain terms, an innocent puppy murmur is usually a soft whooshing or swishing sound layered over the first heartbeat, sometimes with a musical or vibrating quality. A patent ductus arteriosus sounds different: a continuous washing-machine or machinery murmur that runs through both parts of the beat, heard high on the left chest. A leaking or narrowed valve tends to sound harsher and more blowing.

Veterinarians grade murmur loudness on a six-point scale. The grade describes volume, not danger.

Grade	What the veterinarian hears
I	Very faint, audible only after listening carefully in a silent room
II	Soft but heard straight away, usually in one small area
III	Moderate, easily heard, no vibration felt through the chest
IV	Loud, heard over a wide area, still no palpable thrill
V	Loud, with a thrill that can be felt with a hand on the chest
VI	Loud enough to hear with the stethoscope lifted off the chest wall

So a grade 1 puppy heart murmur is a faint sound that is statistically more likely to be innocent, and many of them disappear by the time the puppy is spayed or neutered. A grade 2 murmur is soft but consistent and still sits in the range where innocent murmurs commonly fall. A grade 3 murmur sits at the boundary: innocent murmurs are rarely that loud, so most veterinarians will recommend imaging rather than waiting. Anything at grade 4 or above, or any murmur with a thrill, is treated as structural until an echocardiogram says otherwise.

The trap worth knowing is that loudness and severity are not the same thing. Some serious lesions produce surprisingly quiet murmurs, especially when the heart is already struggling to generate flow. A quiet murmur is reassuring, not conclusive.

Symptoms to watch at home, and the signs that mean emergency

A puppy with an innocent murmur looks like any other puppy: eats well, gains weight, plays hard, sleeps hard, recovers quickly. There are no symptoms, because there is nothing wrong.

Things worth reporting to your vet promptly include tiring faster than littermates or sitting down during play, poor weight gain or looking smaller than the rest of the litter, a persistent cough, breathing faster than normal while asleep, a swollen or fluid-filled belly, or reluctance to exercise at all.

Go to an emergency veterinarian now if your puppy collapses or faints, has gums that look pale, grey or blue, is breathing with open mouth or obvious effort while resting, or has hind-limb weakness that comes on suddenly. These are not symptoms to photograph and ask about in a forum thread later.

Should you bring home a puppy with a murmur?

This is the question that brings most people to the internet at 11pm, and the honest answer is that a murmur by itself is not a reason to walk away, and it is also not something to shrug off because the breeder says they all have it.

What changes the decision is information. Before you commit, ask when the murmur was first heard and by whom, ask for the grade, and ask whether an echocardiogram has been done. If it has not, arrange one with a veterinary cardiologist and make the sale conditional on the result if the breeder or shelter will agree. Ask whether either parent or any littermates have been screened. Find out whether pet insurance can be arranged before a diagnosis is recorded, because a murmur noted in the file first can be excluded as a pre-existing condition later.

Then be realistic with yourself about money and emotion. A puppy with a correctable defect may need a procedure that costs a significant amount, and a puppy with a severe lesion may need lifelong monitoring. Those costs vary widely by region, by clinic and by whether a specialist centre is involved, so get a written estimate rather than relying on a figure from a forum. Plenty of people take the puppy anyway and never regret it. The goal is to make that choice with the echo results in hand rather than in the car park.

Testing, treatment options and what life expectancy really depends on

The definitive test is a Doppler echocardiogram, an ultrasound of the beating heart, usually performed by a veterinary cardiologist. It shows the structure, measures flow speed and pressure gradients, and gives the lesion a severity rating. Chest radiographs, an ECG and blood pressure measurement may be added. Some puppies with soft, low-grade murmurs and no other findings are simply rechecked at the next vaccine visit and again after five or six months of age to confirm the sound has gone.

Treatment depends entirely on the diagnosis. Innocent murmurs need nothing at all. A patent ductus arteriosus is typically closed, either with a catheter-delivered occluding device or by surgical ligation, and closing it early, before the heart has remodelled around the extra workload, is generally considered the priority. Severe pulmonic stenosis may be addressed with balloon valvuloplasty. Some lesions are managed with medication rather than a procedure, and small ventricular septal defects are sometimes just monitored. Every one of those decisions belongs to your veterinarian and the cardiologist, not to a checklist online.

On life expectancy: the grade of the murmur tells you very little. A puppy with a loud grade 4 murmur from a successfully closed ductus can go on to a normal, long life, while a quieter murmur from severe subaortic stenosis carries a far more guarded outlook. What matters is the specific lesion, its severity grading on the echo, and how early it is addressed. Ask your cardiologist for the outlook for your puppy's specific diagnosis, and understand that results vary from dog to dog.

Key Takeaways

• Murmurs are common findings in puppies, and many are innocent flow murmurs that fade as the puppy grows, often by four to six months.
• The grade (I to VI) measures loudness, not seriousness. Soft murmurs are more often innocent, but severity is decided by imaging.
• Innocent murmurs cause no symptoms. Poor growth, early fatigue, coughing, fast resting breathing, fainting or pale gums all warrant urgent veterinary attention.
• An echocardiogram with a veterinary cardiologist is the only test that identifies the cause.
• A murmur does not automatically mean you should pass on a puppy, but get the echo, the grade and an insurance decision sorted before you commit.
• Life expectancy depends on the underlying defect and how early it is addressed, not on how loud the murmur sounds.

If you are trying to judge how fast to act on something you are seeing at home, it is worth knowing which signs are genuine red flags: Dog Emergency Signs covers the symptoms that mean the same-day or after-hours clinic rather than the next routine appointment.

Your veterinarian owns this. They are the one who grades the murmur, decides whether an echocardiogram is warranted, refers to a cardiologist, and builds the monitoring or treatment plan around what the imaging shows. Bring your notes, your questions and anything you have recorded at home, talk to your vet about what the findings mean for your particular puppy, and let the diagnosis come from the stethoscope and the ultrasound rather than from a search result.