Heart Murmurs in Cats: Harmless or a Sign of Disease?

Nov 05 • 10 min read

Your vet paused mid-exam, listened again, and said the word "murmur." Your cat, meanwhile, is sitting there looking completely unbothered maybe even a little annoyed at being handled for this long. That contrast is genuinely confusing, and it's actually the whole point of this topic: a heart murmur in a cat tells you almost nothing on its own. It's a clue, not a diagnosis, and roughly half the time, it turns out to mean nothing serious at all.

A heart murmur is an abnormal "whooshing" sound caused by turbulent blood flow through the heart or its major vessels, and in cats specifically, murmurs are genuinely tricky to interpret some are harmless, and some cats with serious underlying heart disease have no murmur at all. Cats are famously good at hiding illness, and heart disease is one of the areas where that tendency matters most: many cats with real heart changes look and act completely normal until a vet happens to hear something unexpected during a routine exam.

Key Takeaways

A heart murmur is a "whooshing" sound caused by turbulent blood flow, graded on a loudness scale from I (barely audible) to VI (audible without a stethoscope).
Murmur loudness does not reliably predict severity a loud murmur can come from a minor issue, and a serious heart condition can exist with no murmur at all.
"Innocent" murmurs are common in young kittens (usually appearing around 6 to 8 weeks and resolving by 4 to 6 months) and can also appear temporarily in stressed adult cats.
Hypertrophic cardiomyopathy (HCM) is the most common heart disease found in cats with a murmur, and many affected cats show no other signs at home for months or years.
Maine Coons and Ragdolls carry a known inherited risk for certain forms of cardiomyopathy, though any cat, including mixed breeds, can be affected.
Diagnosis usually needs more than a stethoscope bloodwork, blood pressure, chest X-rays, and an echocardiogram are the tools that actually confirm what's going on.

What Is a Heart Murmur, Exactly?

Infographic showing the Grade I to VI heart murmur loudness scale used in cats

A heart murmur is an abnormal heart sound, heard when blood flows through the heart's chambers with more turbulence than normal, creating a "whooshing" noise between the heart's normal "lub-dub" beats. Vets grade murmurs on a scale of roughly I to VI based on loudness: a Grade I murmur is soft and may only be heard intermittently in a quiet room, while a Grade VI murmur is loud enough to be felt through the chest wall without a stethoscope at all.

Does a Louder Murmur Mean a More Serious Problem?

Infographic explaining why heart murmur loudness in cats does not reliably predict disease severity.

Not necessarily, and this is genuinely one of the more counter-intuitive things to understand. The loudness of a murmur reflects how much turbulence is present, not how severe the underlying condition is. A cat can have a loud murmur from a relatively minor issue, and this is the part that surprises most pet parents a cat can have significant, genuine heart disease with no audible murmur whatsoever. Risk does not always equal symptoms, and a murmur does not always equal severe disease, or the reverse. This is exactly why a murmur is treated as a prompt to investigate further, not as a diagnosis in itself.

Are All Heart Murmurs in Cats a Problem?

Genuinely, no. A meaningful proportion of murmurs in cats commonly estimated at around half aren't associated with any underlying heart or vessel disease at all. Of those that are linked to a real cause, many cats go on to live entirely normal lives without ever developing signs of illness.

Innocent Murmurs in Kittens

Young, growing kittens commonly develop what's called an innocent or physiologic murmur, typically appearing around 6 to 8 weeks of age and usually resolving on its own by 4 to 6 months. This type of murmur is benign a byproduct of a young, fast-growing heart pumping blood a little more turbulently than an adult's, not a sign of any structural problem. If your kitten is found to have a soft, low-grade murmur at a young age with no other symptoms, your vet will likely recommend simple monitoring and a recheck rather than immediate advanced testing.

Temporary Murmurs in Adult Cats

Adult cats can also develop a temporary murmur during periods of stress or a fast heart rate — a stressful vet visit is a classic trigger. This kind of murmur typically disappears once the cat calms down and the heart rate returns to normal, and it doesn't reflect any lasting heart problem.

Why Do Cats Hide Heart Disease So Well?

This is genuinely one of the defining challenges of feline cardiology, and it's worth understanding clearly. Cats often hide illness very well, and many cats with real heart disease have no obvious signs early on — some are only identified after a vet happens to hear a murmur, an abnormal "gallop" rhythm, or an irregular heartbeat during a routine exam. Others don't show any clear symptoms until they develop congestive heart failure or a sudden arterial blood clot, both of which can appear seemingly out of nowhere in a cat who seemed completely fine the day before.

Because of this, subtle changes at home genuinely matter more than they might for a dog sleeping more than usual, hiding, eating less, or breathing faster at rest are all worth paying attention to, even when they seem minor or easy to explain away.

What Actually Causes a Pathologic Murmur in Cats?

Heart disease in cats may be primary, meaning it starts in the heart itself, or secondary to another condition entirely, such as hyperthyroidism or high blood pressure. Hypertrophic cardiomyopathy (HCM) a thickening of the heart muscle walls is the most common heart disease diagnosed in cats with a murmur. Anemia, from something like a significant flea infestation, particularly in kittens, can also produce a murmur by making the blood flow more turbulently than normal, without the heart itself being structurally diseased at all.

Does Breed Matter?

Yes, genuinely, though it's not the whole picture. Some breeds, including Maine Coons and Ragdolls, have a known inherited risk for certain forms of cardiomyopathy. Still, any cat can be affected, including mixed-breed cats breed risk is a useful piece of context, not a reliable filter for who needs to be taken seriously.

How Are Heart Murmurs in Cats Diagnosed?

A murmur alone doesn't tell your vet what's actually happening inside your cat's heart a proper diagnostic work-up is genuinely necessary to find out. Bloodwork, including a cardiac biomarker called proBNP, blood pressure measurement, and chest X-rays are common starting points, and thyroid testing is often included too, since hyperthyroidism can meaningfully affect the heart in older cats.

Why the Echocardiogram Matters So Much

Veterinary cardiologist performing an echocardiogram on a cat to evaluate a heart murmur.

An echocardiogram an ultrasound of the heart is considered the key, definitive test for confirming most feline heart conditions linked to a murmur, particularly cardiomyopathy. It lets your vet or a veterinary cardiologist see the heart's actual structure and function directly, rather than inferring it indirectly from a sound alone. A calm, stable cat with a newly discovered murmur may only need a straightforward, scheduled outpatient echocardiogram, while a cat showing signs like open-mouth breathing or weakness may need urgent stabilisation and imaging instead the specific approach depends genuinely on how your cat is doing overall, not just on the murmur itself.

A Simple Habit Worth Learning at Home

Given how well cats mask illness, home monitoring genuinely earns its place here. If your vet recommends it, tracking your cat's resting or sleeping breathing rate is a simple, free way to help catch heart failure changes earlier, often before anything dramatic happens. This is worth asking about directly, especially if your cat has a known murmur, a higher-risk breed background, or another condition like hyperthyroidism that can affect the heart.

Questions Worth Asking Your Vet

"Is this murmur likely innocent, or does it warrant further testing?" Your cat's age, the murmur's grade, and whether other signs are present all genuinely factor into this answer.
"Should we do an echocardiogram now, or monitor and recheck first?" For a calm, asymptomatic cat, either approach can be reasonable the right choice depends on your cat's specific situation.
"Could an unrelated condition anemia, hyperthyroidism, high blood pressure be causing this murmur?" Ruling these in or out changes the whole direction of the work-up.
"What breathing rate or behaviour change at home should prompt a call?" Given how quietly cats can decline, having a specific number and pattern to watch for is genuinely more useful than a vague "let me know if anything seems off."

Living With a Cat Who Has a Heart Murmur

Don't panic at the word "murmur" alone. As covered above, roughly half of all feline murmurs aren't linked to any underlying disease, and many cats with a genuine cause still live long, comfortable lives.
Don't assume a calm cat is automatically a healthy cat, either. Because cats hide illness so well, a proper diagnostic work-up matters even when your cat seems completely fine.
Watch for the subtle signs, not just dramatic ones — sleeping more, hiding, eating less, or breathing faster at rest are all genuinely worth mentioning to your vet.
If your cat is a Maine Coon or Ragdoll, be aware of the documented inherited cardiomyopathy risk in these breeds, and ask your vet about screening timing.
Feed a complete, properly formulated commercial cat food. Taurine deficiency historically caused some cases of dilated cardiomyopathy in cats, and while it's now uncommon with good commercial diets, unbalanced homemade or nontraditional diets can still create real problems.
Watch the wider picture. Our guide on 10 signs your pet is sick and our guide on cat not eating but active — should I worry? both cover the kind of subtle behaviour changes worth tracking alongside a known murmur.
Never self-medicate a cat with a heart condition. Our guide on human medicines and pets explains why this is genuinely dangerous territory for any cat with a cardiac diagnosis.
If your cat needs ongoing medication, our guide to giving cats medicine covers a calm, effective technique for long-term treatment plans.

FAQ

Should I be worried if my kitten has a heart murmur?
Not necessarily, especially if your kitten is young, the murmur is soft, and there are no other symptoms this pattern often fits an innocent murmur that resolves by 4 to 6 months of age on its own. Your vet will likely recommend a recheck rather than immediate advanced testing in this specific situation.

Can a cat have serious heart disease without a murmur?
Yes, genuinely this is one of the more important, counter-intuitive facts in feline cardiology. Significant heart disease can be present without ever producing an audible murmur, which is exactly why routine exams, bloodwork, and imaging all matter, not just listening with a stethoscope.

What's the most common cause of a heart murmur in an adult cat?
Hypertrophic cardiomyopathy (HCM) is the most common heart disease diagnosed in cats with a murmur. Many affected cats stay in a subclinical phase for months or even years, showing no obvious symptoms at home despite genuine changes happening inside the heart.

Is an echocardiogram always necessary if my cat has a murmur?
Not always immediately a calm, asymptomatic cat with a soft murmur may be monitored and rechecked first, while a cat with any concerning signs, a loud murmur, or a higher-risk breed background may be referred for an echocardiogram sooner. This is genuinely a conversation to have directly with your vet based on your cat's specific picture.

Can stress alone cause a heart murmur in a cat?
Yes some healthy adult cats develop a temporary murmur when their heart rate rises due to stress, such as during a vet visit, and it disappears once the cat calms down. This is one reason your vet may want to re-examine a nervous cat again later, in a calmer state, before drawing conclusions.