What is a heart murmur in dogs?

A heart murmur in a dog is something an owner may notice as an unexpected sound, a change in energy, or a new cough. This article explains what murmurs are, why they matter, how they happen, and practical steps you can take if you suspect your dog has one. Expect clear, actionable guidance you can use when talking with your veterinarian.

Why a heart murmur matters for your dog’s health — and your peace of mind

Recognizing a possible heart murmur matters because it often marks the first sign of heart trouble that, if addressed early, may be managed to preserve your dog’s comfort and lifespan. I typically see owners notice a murmur when they bring a puppy in for vaccination checks, when a middle‑aged dog has a new cough, or when a senior begins to tire more quickly on walks. For breeders, identifying congenital murmurs early is critical for responsible breeding choices.

Ignoring or delaying evaluation can change outcomes. A mild, innocent murmur that is monitored may never limit a dog’s life, while a pathological murmur related to valve disease or a congenital defect is likely to progress if untreated. Early diagnosis often opens options—medication, dietary adjustments, and activity planning—whereas late recognition can lead to hospital visits and urgent interventions. Emotionally, owners who act quickly usually report less anxiety because they understand what to expect and how to help their dog live comfortably.

What a heart murmur actually is: the essentials every owner should know

A heart murmur is an extra or unusual sound made by turbulent blood flow in the heart or nearby vessels; a veterinarian usually detects it by listening with a stethoscope. Not all murmurs mean disease. Some are “innocent” or physiological and may not affect health, while others are pathological and may be linked to structural heart problems such as damaged valves or congenital defects.

Typical first signs owners notice are an odd whooshing sound when a vet listens, increased panting, tiredness during normal activity, a new cough, or fainting episodes. If you or your vet hears a murmur, the immediate next step is a thorough veterinary exam and likely referral for diagnostic tests—don’t assume it’s harmless without at least an initial assessment.

Listening in — how heart sounds are produced and what an abnormal murmur means

A dog’s normal heartbeat produces two clear sounds: the first (soft “lub”) when the heart’s valves close as the ventricles contract to push blood out, and the second (soft “dub”) as the valves close after blood flows into the ventricles. Those sounds reflect smooth, organized blood flow and well‑seated valves. When blood moves in a chaotic or high‑velocity way—around a narrowed valve, leaking valve, or hole between chambers—that turbulence creates an additional sound we call a murmur.

Murmurs may arise for different mechanical reasons. In older dogs, gradual wear of the mitral valve is common and may be described as degenerative valvular disease. Puppies can have congenital defects such as a ventricular septal defect that allows blood to flow abnormally between chambers. Some murmurs are physiological and linked to temporary states like fever or anemia, where blood flow patterns change but the heart structure is otherwise normal.

The loudness or “grade” of a murmur gives clues but doesn’t tell the whole story. A high‑grade murmur is more likely to be associated with significant heart dysfunction, but I’ve also seen quiet murmurs that accompanied serious underlying disease. Imaging and other tests are needed to understand whether the murmur reflects a problem that requires treatment.

When murmurs commonly appear: age, breed, and typical triggers

Age is a major factor. Puppies may show murmurs at birth or during growth because of congenital heart defects; some of those murmurs resolve as the puppy matures. Adult dogs can develop murmurs from diseases that progress over months to years. Small‑breed dogs often develop degenerative valve disease later in life; large breeds sometimes present with different heart issues at middle age. Seniors have the highest likelihood of newly detected murmurs simply because age‑related changes accumulate.

Activity and exertion can make a previously quiet murmur more noticeable: you might hear heavier breathing or more pronounced signs after a long walk or play session. Medical conditions that change blood characteristics—severe anemia, fever, or active infection—can create or worsen murmurs transiently. Stress, body position, or even excitement during an exam may alter how noticeable a murmur is when a vet listens.

When to worry: red flags and emergency signs to watch for

Some signs suggest an urgent problem and merit immediate veterinary attention. Collapse or fainting (syncope) during activity or at rest is a serious red flag. New or worsening cough, especially if it occurs at night or when the dog lies down, can indicate fluid accumulation in the lungs related to heart failure. Difficulty breathing, open‑mouth breathing in a non‑brachycephalic dog, or blue‑tinged gums (possible low oxygen) are emergencies.

Other worrying changes include sudden, marked weight loss, swelling of the abdomen or limbs (suggesting fluid buildup), rapid or very irregular heartbeat noticed by palpating the chest, and severe lethargy or inability to exercise. If you observe any of these, seek veterinary care promptly rather than waiting for an appointment.

If your vet detects a murmur — clear next steps for owners

If you suspect your dog has a murmur, start by calmly observing and recording what you see: how long episodes last, what triggers them, and whether signs happen at rest or with activity. Note the dog’s age, breed, any known health issues, medications, and recent illnesses. A clear timeline helps your veterinarian prioritize tests and treatments.

Record audio or video when possible—videos of coughing, panting, fainting, or breathing difficulty are especially useful. I often ask owners to bring short clips showing the behavior because one observation in the clinic may miss an intermittent problem. Next, schedule a veterinary exam and describe what you recorded and observed. If your primary vet hears a murmur, expect either immediate diagnostics or a referral to a cardiologist depending on the murmur’s characteristics and your dog’s overall status.

Follow the diagnostic and treatment plan your vet recommends. That may include imaging, bloodwork, medications, or lifestyle changes. Keep a log of symptoms and medication effects, and keep communication open—reports from owners are key to adjusting care over time.

Everyday care and training for dogs with murmurs

Adjusting daily routine can reduce risk and improve quality of life. Modify exercise to match your dog’s tolerance: shorter, more frequent walks, avoiding steep hills or high‑intensity play, and watching recovery time afterward. Teach slow warmups and cool‑downs. If your dog tires quickly, work within those limits and use positive reinforcement to keep training sessions short and stress‑free.

Stress reduction is important because anxiety raises heart rate and respiratory effort; build confidence gradually, avoid sudden changes, and introduce handling and vet visits with patience and rewards. Maintain ideal body weight—obesity stresses the heart—so follow portion guidance and choose diets appropriate for age and activity. Monitor at home for increased coughing, shorter walks, or faster breathing at rest, and report these changes to your vet promptly.

Practical tools and gear: monitors, aids, and what’s worth buying

A few practical items help owners monitor and support dogs with murmurs. A basic stethoscope can let you learn how your dog’s heart sounds at home; I only recommend it if you get some hands‑on guidance from your veterinarian because interpreting what you hear takes practice. A smartphone to record episodes of coughing, difficulty breathing, or fainting is invaluable—timestamped videos provide context that memory alone cannot.

Use a harness instead of a collar to avoid pressure on the neck and chest during walks, especially for dogs with cough or respiratory sensitivity. Medication organizers and phone reminders help keep dosing consistent if medicines are prescribed. Finally, having a logbook—paper or digital—to note changes in exercise tolerance, appetite, and daily breathing patterns makes follow‑up visits far more productive.

Who to consult and which diagnostic tests matter most

Your primary care veterinarian is the first step: they will listen to the heart, evaluate overall health, and decide if advanced testing is needed. If the murmur is suspicious or the dog shows clinical signs, referral to a veterinary cardiologist is often appropriate. Cardiologists specialize in imaging and long‑term management and can guide choices about medications and interventions.

Key diagnostic tools include echocardiography with Doppler, which images heart structure and measures blood flow; chest X‑rays to check heart size and lung condition; and an electrocardiogram (ECG) to detect rhythm problems. Bloodwork can reveal anemia, infection, or organ dysfunction that may influence the heart or treatment. Referral to specialty care is warranted when tests suggest structural disease, when clinical signs are present, or when the primary vet recommends expert input.

Sources and further reading — studies and expert references

• ACVIM Consensus Statement: “Guidelines for the Diagnosis and Treatment of Myxomatous Mitral Valve Disease in Dogs” (Journal of Veterinary Internal Medicine, ACVIM, 2019)
• Merck Veterinary Manual: “Cardiac Murmurs in Dogs” — Merck Vet Manual (specific clinical overview and management guidance)
• AVMA Client Information: “Heart Disease in Dogs” — American Veterinary Medical Association client education materials
• Borgarelli M, Buchanan JW. “Degenerative mitral valve disease in dogs” — review in the Journal of Veterinary Cardiology and related peer‑reviewed literature