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Heart Murmurs in Dogs: Symptoms, Causes, Treatment, and Prevention

A heart murmur in dogs is an abnormal whooshing or swishing sound heard between normal heartbeats, caused by turbulent blood flow, and it’s a finding rather than a disease in itself, meaning its significance depends entirely on what’s causing it.

A murmur detected in a puppy is often a harmless, temporary finding, while the same sound in a senior small-breed dog is more likely to signal underlying heart disease, which is why the same exam finding can mean very different things depending on the dog. This guide covers what causes heart murmurs, their symptoms, how they’re diagnosed, how they’re treated, whether they can be prevented, and when to see a veterinarian.

This guide covers what a heart murmur is, what causes it in dogs, its symptoms, how it’s diagnosed, how it’s treated, whether it can be prevented, when to see a vet, and what else people ask.

What Is a Heart Murmur in Dogs?

A heart murmur is an abnormal sound, often described as a whooshing or swishing noise, heard through a stethoscope between the normal heart sounds, caused by turbulent rather than smooth blood flow through the heart. Veterinarians grade murmurs on a scale from one to six based on loudness, with a higher grade generally, though not always, correlating with more significant underlying turbulence. A murmur itself is a physical exam finding rather than a diagnosis, and its true significance depends on identifying what’s causing the turbulent blood flow in the first place.

What Causes Heart Murmurs in Dogs?

Many puppies have what’s called an innocent or physiologic murmur, a soft, typically low-grade sound that reflects normal developmental blood flow patterns and usually resolves on its own by around four to five months of age without any underlying heart disease. In adult and senior dogs, murmurs more often reflect actual structural heart disease, including mitral valve disease, dilated cardiomyopathy, or a congenital heart defect present since birth. Non-cardiac conditions, including significant anemia or certain systemic illnesses, can also produce a murmur by altering how blood flows through an otherwise structurally normal heart.

What Are the Symptoms Associated With a Heart Murmur in Dogs?

A heart murmur itself doesn’t directly cause symptoms, since it’s simply a sound reflecting how blood is flowing through the heart rather than a condition that produces discomfort on its own. Any symptoms a dog with a murmur shows, including coughing, exercise intolerance, or labored breathing, actually stem from the underlying condition causing the murmur rather than the murmur itself. This is exactly why a dog can have a murmur and show no symptoms at all, particularly in the earlier stages of an underlying heart condition.

How Are Heart Murmurs in Dogs Diagnosed?

A veterinarian detects a heart murmur during a routine physical exam using a stethoscope, noting its grade, location, and timing within the heartbeat cycle, all of which provide clues about the likely underlying cause. For a young puppy with a soft, low-grade murmur, a veterinarian may recommend simply rechecking it at the next visit to see if it resolves on its own. For an adult or senior dog, or any louder or more concerning murmur, an echocardiogram, an ultrasound of the heart, is typically recommended to directly visualize the heart’s structure and determine the murmur’s actual cause.

How Are Heart Murmurs in Dogs Treated?

An innocent puppy murmur typically requires no treatment at all and is simply monitored until it resolves on its own, usually within the first several months of life. A murmur caused by underlying heart disease is treated by addressing that specific condition, whether that’s medication for mitral valve disease or dilated cardiomyopathy, or addressing a non-cardiac cause like anemia directly. There’s no treatment that targets the murmur sound itself, since treatment always focuses on the actual underlying cause once it’s identified.

Can Heart Murmurs in Dogs Be Prevented?

Innocent puppy murmurs aren’t something that needs preventing, since they’re a normal developmental finding that resolves on its own. Murmurs caused by genetic heart disease, including mitral valve disease, generally can’t be prevented, since they stem from a predisposition outside an owner’s control. Regular veterinary wellness exams that include careful heart auscultation give a dog the best chance at having a murmur detected and investigated early, even though the underlying conditions that cause many murmurs aren’t preventable themselves.

When Should You See a Vet for a Heart Murmur in Dogs?

See a veterinarian if a murmur is newly detected in an adult or senior dog, since this is more likely to reflect underlying heart disease than a murmur found in a young puppy. Any dog with a known murmur that develops coughing, reduced exercise tolerance, or labored breathing needs a prompt veterinary evaluation, since these symptoms can indicate the underlying condition is progressing. A puppy with a murmur should be rechecked as recommended by a veterinarian to confirm it resolves as expected rather than assuming it will without follow-up.

What Else Do People Ask About Heart Murmurs in Dogs?

The questions below cover whether all heart murmurs are dangerous, whether murmur grade indicates severity, whether dogs with a murmur can still exercise, and whether murmurs are hereditary.

Are all heart murmurs in dogs dangerous?

No, not all heart murmurs are dangerous; an innocent puppy murmur is harmless and typically resolves on its own, while a murmur in an adult dog caused by significant heart disease carries more serious implications. The underlying cause, not the murmur sound itself, determines how concerning a specific case actually is.

Does a murmur’s grade indicate how severe the underlying problem is?

Generally yes, a higher-grade murmur often correlates with more significant turbulent blood flow, but grade alone doesn’t tell the whole story, since a lower-grade murmur can sometimes still reflect meaningful underlying disease. An echocardiogram provides a far more accurate picture of actual severity than murmur grade alone.

Can dogs with a heart murmur still exercise?

Many dogs with a murmur, particularly an innocent puppy murmur or early-stage heart disease without symptoms, can continue normal exercise, but a veterinarian’s guidance should shape activity level for any dog with a confirmed underlying heart condition. Exercise recommendations become more restrictive as heart disease progresses toward heart failure.

Are heart murmurs hereditary in dogs?

Murmurs caused by inherited heart conditions, including mitral valve disease and certain congenital defects, do have a genetic component and can run in certain breeds and bloodlines. An innocent puppy murmur, by contrast, isn’t a hereditary condition and simply reflects a normal, temporary developmental pattern.

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