Puppy Heart Murmurs: When Should You Worry?

Vet verified. Written by Dr. Alex Crow, Team Vet. Reviewed by Elle Padgham, Communications Lead.

A puppy heart murmur is a sound created by turbulent blood flow, not a diagnosis by itself. Some soft murmurs are innocent and disappear as a puppy matures. Others reflect congenital heart disease, anemia, fever or another condition. The murmur's grade describes loudness and does not reliably predict the exact cause or outcome.

If your veterinarian hears a murmur, ask what was heard, whether the puppy has symptoms and when rechecking or echocardiography is recommended. Difficult breathing, collapse, blue or very pale gums, severe weakness or fainting needs emergency care.

What is a heart murmur in a puppy?

A normal heartbeat produces familiar valve-closure sounds. Turbulent blood flow can add a whooshing sound between or around those beats. A veterinarian listens with a stethoscope and describes timing, location, radiation, pitch and loudness.

A murmur is a finding, not the final answer

The sound confirms that blood flow is audible in an unusual way. It does not tell the owner whether a valve, vessel, chamber or noncardiac condition is responsible. Two puppies with equally loud murmurs can have different causes.

At what age are puppy murmurs found?

Many are first heard during routine examinations in the first weeks or months of life. A soft murmur may change as circulation and body size develop. A murmur that persists, grows louder or occurs with symptoms needs further assessment.

What causes a puppy heart murmur?

Innocent or physiologic flow

An innocent murmur occurs without structural heart disease. These murmurs are generally soft and may disappear by about six months of age. Only follow-up examination can show whether an individual murmur resolves.

Patent ductus arteriosus

The ductus arteriosus is a fetal vessel that should close after birth. If it remains open, abnormal blood flow can create a characteristic murmur and strain the heart. Timely diagnosis matters because selected puppies benefit from closure by a veterinary cardiology team.

Ventricular septal defect

A ventricular septal defect is an opening between the lower heart chambers. The effect depends on its size, pressure difference and other anatomy. A loud sound does not by itself define the clinical impact.

Valve or outflow abnormalities

Malformed valves or narrowing near the heart's outflow can cause turbulence. Examples include pulmonic or subaortic stenosis. Echocardiography is used to view anatomy and measure blood-flow velocity.

Extracardiac causes

Anemia, fever, infection and other high-flow states can produce or change a murmur even when the primary problem is outside the heart. History, examination and appropriate laboratory testing help identify these possibilities.

Innocent versus pathologic murmurs

Innocent murmurs are typically quiet, occur in a characteristic part of the heartbeat and are found in otherwise healthy puppies. Pathologic murmurs result from structural or functional disease. No home checklist can confidently separate them.

How heart murmurs are graded

Veterinarians commonly use a scale from grade 1 through grade 6. This is a loudness scale, not six stages of disease.

Grade 1

Very soft and heard only in a quiet setting by careful listening. A grade 1 murmur can be innocent, but its cause still depends on the complete examination.

Grade 2

Soft but readily heard once the stethoscope is positioned correctly. Many innocent puppy murmurs are low grade, but low grade does not guarantee innocence.

Grade 3

Moderately loud without a palpable vibration. Further evaluation is often recommended based on age, location, timing, persistence and symptoms.

Grade 4

Loud and heard over a broad area of the chest, but without a palpable thrill. It deserves careful investigation.

Grade 5

Very loud with a thrill, which is a vibration felt on the chest. The sound remains audible with the stethoscope partly lifted from the chest.

Grade 6

The loudest grade, with a thrill and sound audible even when the stethoscope is lifted slightly away. Urgent cardiology assessment is appropriate, but the diagnostic test still determines the cause.

Why murmur grade is not disease severity

The amount of turbulence and pressure difference influence loudness. A small opening can sometimes make a loud sound, while advanced disease may not produce the loudest murmur. Never use grade alone to predict life expectancy or treatment.

Symptoms to watch for at home

• Rapid or labored breathing at rest
• Poor growth or difficulty gaining weight
• Unusual fatigue, weakness or reduced play tolerance
• Coughing or repeated breathing changes
• Fainting, collapse or blue or very pale gums
• A swollen abdomen or marked restlessness

Many puppies with murmurs show no outward symptoms. Absence of symptoms does not establish that the murmur is innocent.

When a puppy murmur is an emergency

Go to an emergency veterinary hospital for open-mouth or labored breathing at rest, blue or gray gums, collapse, fainting, severe weakness or sudden inability to exercise. Keep the puppy calm and call ahead while traveling.

How a veterinarian detects a murmur

History and physical examination

The veterinarian asks about growth, energy, breathing, cough, fainting, appetite, litter history and family heart disease. Listening from several chest locations helps define the sound and check heart rhythm. Pulses, gum color, breathing and body condition add context.

Repeat auscultation

A soft murmur in a bright, symptom-free puppy may be rechecked after a defined interval. The plan should include a date and the signs that should trigger earlier review. "Wait and see" is not the same as ignoring it.

What an echocardiogram shows

An echocardiogram is an ultrasound examination of the heart. It shows chamber size, wall motion, valve anatomy and blood flow. Doppler measurements help identify abnormal direction and speed. It is the central test for many congenital heart questions.

What chest X-rays show

Radiographs can assess heart silhouette, lung patterns and some vessels. They do not provide the same structural and blood-flow detail as echocardiography. The veterinarian chooses the test based on the clinical question.

What an ECG shows

An electrocardiogram records electrical activity and helps identify rhythm abnormalities. It does not replace an echocardiogram for evaluating most structural congenital defects.

When blood tests are useful

A complete blood count can identify anemia or evidence of infection, and chemistry tests may be appropriate before medication or anesthesia. Cardiac biomarkers can add information in selected cases but do not replace imaging.

Should the puppy see a cardiologist?

Referral is especially valuable for a loud, continuous, unusual or persistent murmur; symptoms; an abnormal pulse; an abnormal chest image; or a breed and family history that raises concern. Owners may also request a cardiology opinion before purchase, anesthesia or breeding decisions.

Treatment for an innocent murmur

An innocent murmur does not need heart medication. It needs the recommended recheck so resolution is documented. Follow ordinary puppy-care advice unless the veterinarian places a restriction.

Treatment for structural heart disease

Treatment depends on the exact defect and its effect on circulation. Options can include monitoring, medication, catheter-based procedures or surgery. Do not start supplements, restrict activity or change sodium intake without the cardiology plan.

Can medication make a murmur disappear?

Medication is prescribed for a diagnosed condition, not to silence a sound. Diuretics, heart drugs and other prescriptions have specific indications and risks. Never give another dog's medication or stop a prescription because the murmur sounds quieter.

Can surgery correct a congenital defect?

Some defects, including many patent ductus arteriosus cases, can be treated successfully with an interventional or surgical procedure. Suitability, timing, risk and prognosis depend on the individual anatomy and specialist assessment.

Exercise and play with a murmur

Do not impose blanket crate rest on every puppy with a murmur. Ask the veterinarian whether activity should change. Stop activity and seek advice for unusual breathlessness, weakness, fainting or delayed recovery.

Feeding a puppy with a murmur

Most growing puppies need a complete and balanced growth diet selected for expected adult size. Do not use a sodium-restricted or homemade cardiac diet unless a veterinary nutrition professional recommends it for a diagnosed condition. Growth and medication can change calorie needs.

Finch & Barker product boundaries

Buying or adopting a puppy with a murmur

Ask for the complete veterinary record, the murmur description, follow-up plan and health history of parents and littermates. Arrange an independent examination and discuss echocardiography before making a decision. Understand likely testing, treatment, insurance exclusions and long-term costs without assuming the worst.

Can a breeder promise the puppy will grow out of it?

No one can guarantee that from a casual listen or a sales conversation. A soft innocent murmur often resolves, but follow-up examination documents the change and imaging identifies structural disease when needed.

Life expectancy with a heart murmur

A puppy with an innocent murmur has a normal outlook once structural disease is excluded and the murmur resolves. With congenital disease, life expectancy ranges widely by defect, severity, timing of diagnosis and response to treatment. The sound alone cannot supply a prognosis.

What percentage of puppy murmurs are innocent?

An often-cited estimate is about 50 to 70 percent, but prevalence changes with age, breed, study population and referral status. A population estimate cannot classify one puppy. Cornell notes that most soft physiologic murmurs are outgrown by about six months, while persistent murmurs warrant echocardiography.

Common myths about puppy murmurs

Myth: every murmur means heart failure

False. Heart failure is a clinical syndrome with specific signs and testing. Many puppies with murmurs are bright, growing and free of heart failure.

Myth: a quiet murmur is always harmless

False. Loudness alone cannot exclude structural disease. Timing, location, pulses, symptoms and imaging matter.

Myth: every murmur needs surgery

False. Innocent murmurs need monitoring, some defects need only follow-up, and others may benefit from medication or a procedure. Diagnosis guides the choice.

Questions to ask at the veterinary visit

• What grade, timing and location did you hear?
• Are the pulses, breathing and growth normal?
• When should the puppy be rechecked?
• Would you recommend echocardiography or cardiology referral now?
• Should exercise, feeding, vaccination or anesthesia plans change?
• Which signs mean same-day or emergency care?

A home monitoring record

Track weight, appetite, energy and any cough, fainting or breathing change. If the veterinary team requests sleeping respiratory counts, ask them to demonstrate exactly how and when to measure. Do not wake or stress the puppy repeatedly to collect data.

Evidence and related puppy guides

Read Cornell University College of Veterinary Medicine guidance on heart murmurs and echocardiography. Continue with our guides to puppy health checks, fast puppy breathing and healthy puppy growth and portions.

Frequently asked questions

Can a puppy grow out of a heart murmur?

Some soft innocent murmurs disappear as the puppy matures. Rechecks or imaging are needed to confirm the cause and resolution.

Does a grade 2 murmur mean mild disease?

No. Grade 2 means the sound is soft. It does not define the underlying anatomy or outcome.

Can a puppy with a murmur be vaccinated?

The veterinarian should make an individual decision based on examination, diagnosis and current health. Do not delay essential care without professional advice.