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A murmur on its own is not an emergency. These are: open-mouth breathing, a resting breathing rate over 40 breaths a minute, blue or grey gums, collapse, or sudden paralysis of the back legs with crying. Any of those in a cat with a known murmur means the heart may be failing — go now, and keep the cat as calm and still as you can on the way. See why is my cat panting for the breathing count.
The short answer: a heart murmur is a sound, not a diagnosis — turbulent blood flow that the vet can hear through a stethoscope. In cats it is a poor predictor either way. In a study of 103 apparently healthy cats, 16 had a murmur and only 5 of those had heart disease; meanwhile 11 of the 16 cats who did have cardiomyopathy had no murmur at all. So a murmur in a healthy-seeming cat is more often innocent than not, and a clear chest does not rule heart disease out. What the murmur does is earn the next step: an echocardiogram (or a proBNP blood test as a screen), plus a thyroid level and blood pressure, because hyperthyroidism, hypertension and anaemia all cause murmurs in cats that go away when the cause is treated. The grade — I to VI — is how loud it is, not how serious.
Written by Marc Brannigan, Co-Founder & CEO of HempMy Pet. Last updated 13 October 2026.
What the Numbers Actually Say
Most pages tell you a murmur "may or may not" mean heart disease. Here is how often, from the one study that checked every cat with an ultrasound.
Of 16 apparently healthy cats with a murmur, 5 had cardiomyopathy and 11 did not. Two-thirds of murmurs in cats who seem well are innocent, or come from something other than the heart muscle.
Of 16 cats with cardiomyopathy, 11 had no murmur. The stethoscope caught 31% of heart disease. This is why "the vet didn't hear anything" is reassuring but not proof.
Sixteen of 103 cats who seemed fine had it — almost all hypertrophic cardiomyopathy (HCM), the thickened-wall form. Cornell puts HCM at up to 15% of all cats. It is common, it is often silent, and it is why the echo matters more than the murmur.
Figures are from Paige et al., Journal of the American Veterinary Medical Association, 2009 — 103 privately owned, apparently healthy cats, each examined and scanned by two investigators independently. HCM prevalence from Cornell's Feline Health Center.
A murmur is neither necessary nor sufficient for heart disease in a cat. It is a reason to look, not a verdict.
What the Grade Means — and What It Doesn't
"Grade four" sounds like a stage of disease. It is a volume setting.
| Grade | What the vet hears | What it tells you |
|---|---|---|
| I | Barely audible; a quiet room and a trained ear | Quiet murmurs in cats are often innocent, intermittent, or caused by stress in the exam room, anaemia or hyperthyroidism. Still worth the thyroid level and blood pressure; echo if it persists or the cat is a breed at risk. |
| II | Soft but clearly there | |
| III | Moderate — the most common grade | |
| IV | Loud, heard across the chest on both sides | Louder murmurs are more likely to have a structural cause and earn an echocardiogram without waiting. But loudness tracks turbulence, not severity: some of the sickest HCM cats have soft or absent murmurs, and some loud murmurs in kittens are harmless defects that close by six months. |
| V | Loud, with a vibration ("thrill") you can feel on the chest wall | |
| VI | Audible before the stethoscope touches the chest |
Grading definitions follow PetMD's veterinary review. The scale is judged by ear and varies between examiners.
Why a Cat Has a Murmur: The Five Causes
Three of them are not heart disease, and two of those three are fixable.
- Innocent (physiologic). Turbulent flow in a normal heart. Common in kittens, in lean cats, and in a stressed cat whose heart is pounding in the exam room. Often intermittent — there one visit, gone the next. Needs no treatment, but a persistent one in an adult still earns an echo once.
- Hyperthyroidism. In cats over ten, this is the one to check first. An overactive thyroid drives the heart fast and hard, thickens the muscle and produces a murmur — and both the murmur and much of the thickening reverse when the thyroid is treated. One blood test.
- Anaemia or high blood pressure. Thin blood flows turbulently; high pressure strains the heart. Both produce murmurs that resolve when the cause does. A blood count and a blood pressure cuff.
- Hypertrophic cardiomyopathy (HCM). The heart wall thickens, the chamber shrinks, and the heart cannot fill properly. The commonest feline heart disease, genetic in Maine Coons and Ragdolls, often silent until it is not. Diagnosed only by echocardiogram. Many cats live for years with mild HCM; the risks are congestive heart failure and clots.
- Congenital defects and valve disease. Holes between chambers, a vessel that did not close at birth, leaky or narrowed valves. Found in kittens and young cats; some close on their own, some need a cardiologist.
What Happens Next: The Work-Up
If your vet heard a murmur today, this is the order things usually go in, and why.
Cheap, same-day, and they find the three reversible causes. In a cat over ten, a thyroid level is not optional. If the cat is a kitten, the vet may simply recheck in a few months to see whether it has gone.
Measures stretch on the heart muscle. A low result in a cat with no symptoms makes heart disease unlikely and can reasonably defer the echo; a high one means scan now. It is a screen, not a diagnosis.
The ultrasound of the heart is the only test that says whether the muscle is thickened, the chambers enlarged, or the valves leaking — and therefore whether this is a murmur to forget or a disease to manage. Often done by a cardiologist; no anaesthesia needed.
Your Job at Home: Count the Breaths
For a cat with a murmur — diagnosed or not — this is the single most useful thing an owner can do, and almost no page tells you.
Heart failure in cats announces itself as fluid in or around the lungs, and the earliest sign is a faster resting breathing rate — days before anything you would call "breathing trouble." Count the breaths while the cat is asleep: one rise and fall of the chest is one breath. Thirty seconds, double it. Under 30 a minute asleep is normal. Do it a few times a week and write it down so you know your cat's baseline. If it climbs over about 35–40 at rest, or jumps from the usual number, call the vet that day — with a known murmur or HCM, that is the number that gets a cat into treatment early rather than into the emergency room at 2 a.m. The method is on VCA's home breathing-rate page, and we go through it step by step in why is my cat panting.
Where Hemp Fits — and Where It Doesn't
We make hemp products for cats, so here is the straight answer.
A murmur is a sound. Nothing you give changes it, and nothing should delay the thyroid test and the echo. There is no feline evidence that hemp affects heart muscle thickening, valve disease or heart failure, and we are not going to imply otherwise.
Cats with HCM are often on clopidogrel, a beta-blocker, or diuretics. Hemp can change how the liver clears other drugs. If your cat is on cardiac medication, the supplement conversation is your cardiologist's to have, not ours — read is CBD safe for cats first.
A stressed cat has a racing heart and a louder murmur, which makes exams and echoes harder to read. Predictable stress is where a calming supplement has any role in cats — thin feline evidence, lower and slower servings. Mention it to the vet beforehand; some prefer gabapentin before a cardiac visit instead. See hemp for cat anxiety.
The cat serving guide works from body weight; cats handle hemp differently from dogs, which is why the servings are lower. Our cat safety entry lists the carriers and essential oils that are not safe for cats.
For vet-visit stress only — never as a substitute for the echo, and only after you have asked your vet
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When to Call the Vet
Go now if:
- Open-mouth breathing, or a resting breathing rate over 40
- Blue, grey or very pale gums
- Collapse or fainting
- Sudden back-leg paralysis with crying — a clot from the heart (saddle thrombus); see stroke vs seizure in cats
Book this week if:
- A murmur was heard and no thyroid level, blood pressure or echo has been done yet
- The resting breathing count has crept up over a few days, even without obvious distress
- A cat with a known murmur is sleeping more, eating less, or hiding
- Your cat is a Maine Coon, Ragdoll, Sphynx or British Shorthair with any murmur — the HCM breeds
Frequently Asked Questions
Can a cat recover from a heart murmur?
Yes, when the murmur has a reversible cause. Murmurs from hyperthyroidism, anaemia, high blood pressure or exam-room stress resolve when that is treated or passes; innocent murmurs in kittens often disappear as they grow, and some small congenital defects close by around six months. A murmur caused by hypertrophic cardiomyopathy or valve disease does not go away, but the disease behind it can often be managed for years. The echocardiogram is what tells you which kind you have.
What is the average lifespan of a cat with a heart murmur?
There is no single number, because the murmur is not the disease. A cat with an innocent murmur, or one from a treated thyroid, has a normal lifespan. A cat with mild hypertrophic cardiomyopathy and no symptoms often lives for years, sometimes a full life. The outlook shortens once there is congestive heart failure or a clot, which is why the home breathing count matters — it catches failure early, when treatment buys the most time. Ask your vet about the echo findings, not the murmur grade.
When to worry about a heart murmur?
Worry about symptoms, not the sound: a resting breathing rate over 30–35 while asleep, open-mouth breathing, fainting, sudden weakness or paralysis in the back legs, or a cat who is hiding and off food. Also take a murmur more seriously in a cat over ten with weight loss (hyperthyroidism), in a loud grade IV–VI murmur, and in HCM breeds such as Maine Coons and Ragdolls. A quiet, intermittent murmur in a well kitten is the least worrying kind — and still worth one echo if it persists.
What are stage four heart murmurs for a cat?
"Stage four" usually means a grade IV murmur on the I–VI loudness scale: loud enough to be heard clearly across the chest on both sides, but without the vibration you can feel through the chest wall that marks grades V and VI. Grade is volume, not severity. A grade IV murmur earns an echocardiogram promptly because louder murmurs are more likely to have a structural cause, but some cats with serious HCM have grade I murmurs or none at all, and some grade IV murmurs in kittens are defects that close on their own.
Does a heart murmur mean my cat has HCM?
Not usually. In a study of 103 apparently healthy cats, 16 had a murmur and only 5 of those had cardiomyopathy — about one in three. The reverse is also true: 11 of the 16 cats with cardiomyopathy had no murmur. A murmur raises the question; only an echocardiogram answers it. In cats over ten, check the thyroid first, because an overactive thyroid produces both a murmur and a thickened heart that largely reverse with treatment.
What tests will the vet do for a heart murmur?
Usually in this order: blood pressure, a thyroid level and a blood count in the room, because hypertension, hyperthyroidism and anaemia cause murmurs that resolve when treated; then a proBNP blood test as a screen for heart-muscle strain; then an echocardiogram — the ultrasound that actually shows the heart's structure and is the only way to diagnose or rule out cardiomyopathy. Chest X-rays are added if fluid in the lungs is suspected. None of it needs anaesthesia.
How do I monitor my cat with a heart murmur at home?
Count the resting breathing rate while the cat is asleep: chest rises in 30 seconds, doubled. Normal is under 30 a minute. Do it a few times a week and write it down so you have a baseline; if it climbs over about 35–40 at rest or jumps from the usual number, call the vet that day. Also watch for hiding, reduced appetite, sleeping more, and any weakness in the back legs. This single habit is how early heart failure gets caught before it becomes an emergency.
Can hemp or CBD help a cat with a heart murmur?
Not the murmur or the heart disease behind it — there is no feline evidence that hemp affects heart muscle thickening, valves or heart failure, and nothing should delay the thyroid test and the echo. If your cat is on cardiac medication such as clopidogrel, a beta-blocker or a diuretic, hemp can change how those drugs are cleared, so it is your cardiologist's call. The one narrow use is predictable stress, such as before a cardiac visit, with cat-specific servings and the vet's knowledge.
The Short Version
A heart murmur in a cat is a sound, not a diagnosis, and a poor predictor either way: about one in three murmurs in healthy cats turns out to be heart disease, and about two in three cats with heart disease have no murmur. The grade is loudness, not severity. In a cat over ten, check the thyroid first; in any cat, the echocardiogram is the answer. Then count the resting breaths — under 30 asleep — because that is how heart failure is caught early.
Hemp has no role in the murmur or the disease, needs a cardiologist's sign-off alongside heart medication, and fits only the narrow corner of vet-visit stress.
Hemp for Cats → Why Is My Cat Panting
Cat Panting · Stroke vs Seizure · Clingy Cat · Is CBD Safe for Cats · Cat Safety
Marc co-founded HempMy Pet in 2016 with his wife Natalie, the company's COO. HempMy Pet breeds its own hemp genetics, grows them on its certified-organic Colorado farm, and formulates every batch in-house under human-grade standards — seed to sale, nothing sourced overseas. Every batch is third-party tested and the certificates of analysis are published. More about us.
HempMy Pet ran its own 90-day study of 37 dogs with chronic joint discomfort. Of the 32 that completed it, 30 (93%) showed a benefit, and 94% of owners reported their dog's quality of life had improved. It was overseen by Dr. Robin Downing, DVM, MS of the Downing Center for Animal Pain Management, with Lori Kogan, Ph.D. and Peter W. Hellyer, DVM of Colorado State University's College of Veterinary Medicine & Biomedical Sciences, and published in the Journal of the American Holistic Veterinary Medical Association. Read the methodology.
Why Dr. Downing: in 2005 she became only the third veterinarian in the world credentialed as a Diplomate of the American Academy of Pain Management. She founded the International Veterinary Academy of Pain Management, is a Diplomate of the ACVSMR, a Certified Veterinary Pain Practitioner and a Certified Canine Rehabilitation Practitioner, and was the AVMA's 2020 Bustad Companion Animal Veterinarian of the Year. Chronic joint pain is her life's work. Read the published paper (PDF).
This article is general information for cat owners, not veterinary advice. It is reviewed and updated as new peer-reviewed evidence is published, and where the evidence is thin or negative we say so.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. This article is general information, not veterinary advice. If your cat is unwell, contact your veterinarian.
