A heart murmur in cats is an extra swishing or whooshing sound your veterinarian hears when listening to the heartbeat with a stethoscope. It is a sign that blood may be flowing in an unusual way, not a diagnosis on its own. Some murmurs are harmless, others point to heart disease in cats, so your veterinarian will usually recommend further tests to understand the cause.
Many cat owners first hear the words "heart murmur" at a routine check-up and feel a wave of worry. The calm, practical truth is that a murmur is information, a clue that guides the next steps, and your veterinarian is the right person to interpret it.
A cat resting comfortably at home.
What is a heart murmur in cats?
A heart murmur in cats is the sound of turbulent blood flow inside or near the heart, heard as a whoosh layered over the normal "lub-dub" beat. A healthy heartbeat sounds clean and rhythmic, while a murmur adds an extra noise that a veterinarian can detect with a stethoscope.
The heart is a pump with chambers and valves that keep blood moving in one direction. When blood passes through a narrowed opening, a leaky valve, or a thickened chamber, it can swirl instead of flowing smoothly, and that swirl is what creates the sound.
A murmur describes a sound, not a specific disease. The same murmur can have very different causes, which is why your veterinarian looks at the whole picture rather than the sound alone.
Is a heart murmur in cats always serious?
No, a heart murmur in cats is not always serious, and many cats with a murmur live comfortably for a long time. Some murmurs are innocent or caused by temporary factors, while others reflect underlying heart disease in cats that needs monitoring or care.
In kittens, a soft murmur can sometimes be "innocent" and fade as they grow. In adult and senior cats, a murmur is more likely to be linked to a structural change in the heart, so it deserves a closer look.
Stress, excitement, fever, anaemia, or an overactive thyroid can also make a murmur louder or bring one out temporarily. Because the cat in the clinic is often nervous, your veterinarian weighs the murmur against the rest of the exam before drawing conclusions.
Whatever the grade, the sensible next move is the same: talk to your veterinarian about what the murmur means for your individual cat.
What causes heart murmurs in cats?
Heart murmurs in cats are most often caused by changes in the heart muscle or valves, with thickening of the heart wall being one of the more common findings in adult cats. Causes outside the heart, such as anaemia or thyroid changes, can also produce a murmur.
Common contributing factors in cats include:
- Thickening or structural change in the heart muscle (a common finding in adult and senior cats)
- Leaky or narrowed heart valves that disturb smooth blood flow
- Congenital differences a kitten is born with
- Anaemia, where thinner blood flows more turbulently
- An overactive thyroid gland, which is common in older cats
- High blood pressure, which often overlaps with kidney changes
Because the thyroid, blood pressure, and kidneys are all linked to feline heart health, your veterinarian may check these together. If your cat also has kidney concerns, our guide to kidney failure in cats explains how these systems connect.
Only your veterinarian can pinpoint which cause applies to your cat, so any murmur is a reason to book a proper work-up rather than to guess at home.
How do vets grade a heart murmur in cats?
Veterinarians grade a heart murmur in cats on a scale from 1 to 6, where grade 1 is very faint and grade 6 is loud enough to feel through the chest wall. The grade describes how loud the murmur is, not how sick the cat is.
A louder murmur does not always mean worse disease, and a quiet murmur does not always mean the heart is fine. This is a well-known quirk of cats, so your veterinarian uses the grade as one clue among many.
| Murmur grade | What it usually means | What the vet typically does |
| Grade 1 to 2 | Soft, sometimes hard to hear | Notes it, may recheck and consider further tests |
| Grade 3 to 4 | Clearly audible | Often recommends imaging and further work-up |
| Grade 5 to 6 | Loud, may be felt on the chest | Prompts prompt further investigation |
The grade is a starting point for conversation, not a final verdict. Ask your veterinarian to explain what your cat's specific grade means in the context of the full exam.
How do vets diagnose the cause of a heart murmur in cats?
Veterinarians diagnose the cause of a heart murmur in cats using a physical exam plus tests such as an echocardiogram (heart ultrasound), which shows the heart's structure and how it moves. Blood tests, blood pressure checks, X-rays, and an ECG may be added depending on what the vet finds.
A typical diagnostic path for a cat with a murmur looks like this:
- A full physical exam, listening to the heart and lungs and checking the whole cat.
- Blood tests, which can screen for anaemia and thyroid changes and support overall cat heart health.
- Blood pressure measurement, since high blood pressure can affect the heart.
- An echocardiogram, considered the most useful single test for seeing the heart's structure.
- Chest X-rays and sometimes an ECG, to assess heart size, the lungs, and the rhythm.
The echocardiogram is especially helpful because it shows the heart walls, chambers, and valves in real time. This is how a veterinarian tells an innocent murmur apart from a murmur linked to heart disease in cats.
Not every cat needs every test on day one. Your veterinarian will choose the right combination for your cat and may spread tests over more than one visit to keep stress low.
What are the signs of heart disease in cats to watch for at home?
Signs of heart disease in cats can be subtle, and cats are very good at hiding illness, so changes at home matter. Watch for faster or laboured breathing at rest, reduced energy, hiding, poor appetite, or sudden weakness in the back legs.
Early and later signs often differ, and knowing the contrast helps you describe things clearly to your veterinarian.
| Stage | What you might notice at home |
| Early or hidden | A murmur found at check-up, slightly less play, no obvious symptoms |
| More advanced | Faster breathing at rest, open-mouth breathing, lethargy, poor appetite |
| Urgent | Struggling to breathe, collapse, or sudden hind-leg weakness or pain |
A simple home habit for both cats and dogs is to count breaths while your pet rests or sleeps, then share that number with your veterinarian. A steady rise in resting breathing rate is worth a phone call.
If your cat is struggling to breathe, is collapsing, or suddenly cannot use the back legs, treat it as an emergency and contact a veterinarian straight away. For everything milder, note what you see and talk to your veterinarian at the next opportunity.
What should I do next if my cat has a heart murmur?
If your cat has a heart murmur, the best next step is to follow your veterinarian's recommended tests so the cause can be identified, then set up a monitoring plan together. A murmur with no confirmed disease may simply need periodic rechecks, while a confirmed heart condition is managed with a longer-term plan.
Practical steps you can take for your cat:
- Keep every recheck and testing appointment your veterinarian recommends.
- Track your cat's resting breathing rate and energy, and note any changes.
- Keep your cat at a healthy weight and reduce household stress where you can.
- Give any medicines exactly as your veterinarian directs, and never start or stop one on your own.
- Bring a written list of questions to each visit so nothing gets forgotten.
Supporting overall wellbeing in a senior cat often means caring for several organs at once, since the heart, kidneys, and liver are connected. You can read more about that whole-body approach in our overview of three key supplements for heart, kidney and liver support, written for dogs but helpful for understanding the concept across cats and dogs.
Every care plan is individual, so your veterinarian remains the decision-maker about what your particular cat needs.
Where does prescription heart medicine fit in?
For some cats and dogs with confirmed heart disease, a veterinarian may decide that prescription medicine is part of the plan. HeartRx is a prescription heart medicine (pimobendan) your veterinarian may prescribe, so a veterinarian decides whether it fits your pet and how it is given.
HeartRx is prescription only, which means it is never something to start on your own or buy without a veterinarian's involvement. The decision depends on the exact diagnosis, the stage of the condition, and your cat's overall health.
If you would like background reading while you prepare questions for your vet, see what owners should know about HeartRx (pimobendan) and why HeartRx is designed for cats and dogs. These explain the role of the medicine in plain language.
Because pimobendan is prescription only, the right move is always a conversation with your veterinarian, who will match any medicine to your cat's specific diagnosis.
Caring for the whole senior cat
Many cats with a heart murmur are senior, and senior cats often have more than one thing going on at once. Keeping an eye on kidney health and hydration alongside the heart gives your cat the best quality of life.
If your cat also has kidney changes, a veterinary renal diet and supportive care matter, and you can learn more in our article on supporting kidney health in cats and dogs. Always coordinate any supplement with your veterinarian so everything in the plan works together.
Whole-cat care, regular check-ups, good nutrition, hydration, and a calm home, supports comfort over the long run for both cats and dogs. Your veterinarian ties these threads together into one plan.
FAQ
Can a cat live a normal life with a heart murmur?
Yes, many cats live comfortably with a heart murmur, especially when it is innocent or linked to a condition that is being monitored. The key is identifying the cause with your veterinarian and following the recommended recheck and care plan.
Does a louder heart murmur mean worse heart disease in cats?
Not necessarily, because in cats the loudness of a murmur does not reliably match the severity of heart disease. A quiet murmur can still matter and a loud one can be manageable, so your veterinarian relies on tests like an echocardiogram rather than volume alone.
What test best shows the cause of a feline heart murmur?
An echocardiogram, which is an ultrasound of the heart, is the most useful single test because it shows the heart's structure and movement in real time. Your veterinarian may add blood tests, blood pressure checks, X-rays, or an ECG to complete the picture.
Can I give HeartRx to my cat without seeing a vet?
No, HeartRx is a prescription heart medicine (pimobendan) that only a veterinarian can prescribe after diagnosing your cat. Never start, stop, or change a heart medicine on your own.
How often should a cat with a heart murmur be rechecked?
There is no single schedule that fits every cat, because it depends on the cause and stage of the condition. Your veterinarian will set a recheck interval for your individual cat, and you should keep those appointments and report any changes in breathing or energy between visits.
If your cat has just been diagnosed with a heart murmur, you do not have to navigate it alone. Learn more about the available options and how a veterinarian-guided plan can support your cat's heart health when you explore RX Sciences and reach out to our team, and bring your questions to your own veterinarian, who remains at the centre of every decision for your pet.
