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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsHearing that your cat has a heart murmur can sound alarming, but a murmur is a physical finding, not a diagnosis. It is an extra sound caused by turbulent blood flow; some murmurs are harmless, while others are associated with heart disease or a noncardiac condition. Your veterinarian will interpret it alongside your cat’s symptoms and examination findings.
The murmur’s loudness alone cannot show how serious a condition is. Its timing, location, quality, heart rhythm, pulse strength, and your cat’s overall condition help determine what to investigate.
What a heart murmur means
A normal heartbeat produces recognizable sounds as the heart valves open and close. A murmur is an additional whooshing, blowing, or swishing sound caused by turbulent blood flow through the heart or a major blood vessel.
That turbulence can result from:
- Blood moving through an abnormal valve or opening in the heart
- Thickened heart muscle or another structural change
- Blood flowing unusually quickly because of fever, stress, or another illness
- Changes in blood viscosity or protein levels, such as anemia or low blood protein
A murmur may be present with significant heart disease, but it can also occur in a healthy cat. The reverse is also true: some cats with heart disease have no audible murmur.
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Common reasons a cat may have a murmur
1. An innocent or physiologic murmur
Kittens can develop soft murmurs while they are growing rapidly. These are often heard between about 6–8 weeks and 4–5 months of age and may disappear as the kitten matures. Some adult cats also have intermittent murmurs when fear, excitement, or handling raises their heart rate.
These murmurs generally do not affect the cat’s health. A veterinarian may recommend listening again after several weeks rather than immediately performing extensive testing, particularly when the kitten is thriving and the murmur is low-grade and otherwise unremarkable.
2. A congenital heart defect
A cat can be born with an abnormality such as a hole between heart chambers, an abnormal valve, or narrowing in a blood vessel. The effect ranges from minor to serious. A persistent murmur in a kitten should therefore be assessed rather than automatically dismissed as a normal growth-stage sound.
3. Cardiomyopathy, especially HCM
Hypertrophic cardiomyopathy (HCM) is the most commonly diagnosed heart disease in cats. The muscle of the left ventricle becomes abnormally thick, which can interfere with the heart’s ability to fill and pump efficiently.
Some cats with HCM remain apparently well for years. Others develop congestive heart failure or a blood clot that travels to the hind limbs. A murmur may be heard, but its absence does not rule HCM out.
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4. Anemia or low blood protein
When the blood carries less oxygen or has an unusually low protein level, the heart may pump faster or harder. This can create a functional murmur without a primary structural heart problem. In kittens, heavy flea, tick, or intestinal-parasite burdens can contribute to anemia or low protein.
5. Fever, infection, or another temporary illness
Fever and infection can increase blood flow and heart rate enough to produce a murmur. The sound may resolve when the underlying illness is treated.
6. Hyperthyroidism or high blood pressure
Older cats with hyperthyroidism may have a fast heart rate and cardiovascular changes, sometimes including a murmur. High blood pressure can also cause thickening of the heart muscle that resembles or contributes to changes seen with HCM.
7. Body-condition or pregnancy-related changes
Pregnancy, obesity, and severe thinness can alter circulation and make blood flow more turbulent. These possibilities are considered in the context of the cat’s complete examination, not from the murmur alone.
Does the murmur grade tell you how serious it is?
Veterinarians commonly describe murmur intensity on a scale from grade I to grade VI:
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| Grade | Typical description |
|---|---|
| I | Barely audible; may take careful listening to detect |
| II | Soft but readily heard with the stethoscope |
| III | Moderately loud |
| IV | Loud, without a palpable vibration through the chest wall |
| V | Very loud; a vibration may be felt and the sound is heard over much of the chest |
| VI | Extremely loud; audible even when the stethoscope is lifted slightly from the chest |
The grade describes loudness, not disease severity. A quiet murmur may accompany heart disease, while murmur intensity alone cannot establish how serious the underlying condition is. Timing, location, quality, heart rhythm, pulse strength, age, breed, and clinical signs give the veterinarian more useful information.
Signs that make a murmur more concerning
Many cats hide illness, and early heart disease may cause no obvious change at home. Contact your veterinarian promptly if your cat has a murmur and also shows:
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- Reduced appetite, weight loss, weakness, or marked lethargy
- Poor growth or tiring easily in a kitten
- Collapse or fainting
- Pale, gray, or bluish gums
- A swollen abdomen or suspected fluid accumulation
- Sudden painful weakness, dragging, lameness, or paralysis of one or both hind legs
Sudden hind-limb problems can be caused by a blood clot, sometimes called a saddle thrombus, and need urgent treatment.
When breathing is an emergency
Take your cat to an emergency veterinary hospital immediately for open-mouth breathing, obvious breathing distress, blue or gray gums, collapse, or sudden hind-limb paralysis. Do not wait to see whether these signs settle at home, and avoid unnecessary handling or exertion during transport.
To check your cat’s breathing at home, count chest rises while the cat is asleep and not purring. A calm, sleeping cat commonly breathes about 15–30 times per minute, according to VCA Animal Hospitals. A persistent rate above 30 should prompt veterinary advice, particularly if other signs are present. Cornell Feline Health Center notes that cats with congestive heart failure may breathe above 35 times per minute at rest. Counting during purring, after play, or when the cat is frightened will not give a useful baseline.
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How a veterinarian investigates a murmur
The first step is a detailed physical examination. Your veterinarian may ask about exercise tolerance, appetite, breathing, fainting, growth, medications, diet, parasite exposure, and any changes noticed at home. They will assess the murmur’s timing and location, listen for an abnormal rhythm, check pulse quality, and look for signs of anemia or systemic disease.
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Possible tests include:
- Blood tests: These can check for anemia and other systemic illness. Thyroid testing is often relevant for appropriate older cats.
- Chest X-rays: These may show an enlarged heart or fluid in or around the lungs, although normal X-rays do not exclude early heart disease.
- Electrocardiography: An ECG evaluates the heart’s rhythm and electrical activity.
- Echocardiography: An ultrasound examination shows the chambers, valves, heart muscle, and blood flow.
- Doppler echocardiography: Doppler measures the direction and speed of blood flow and is particularly useful for locating the turbulence causing a murmur.
Echocardiography is the gold-standard test for diagnosing feline cardiomyopathies such as HCM. A veterinary cardiologist may perform or interpret the scan, especially when the murmur is persistent, the examination is abnormal, or the cat has symptoms.
A low-grade murmur in an otherwise healthy kitten may be rechecked after several weeks. An adult cat with a murmur, abnormal rhythm, weak pulses, or clinical signs may need more immediate testing.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What happens after diagnosis?
An innocent murmur needs no treatment, although rechecks may be recommended. If anemia, parasites, fever, hyperthyroidism, or another correctable condition is responsible, treatment is directed at that condition.
Heart disease may require medication, monitoring, dietary management, oxygen support during a crisis, or treatment to reduce fluid buildup and blood-clot risk. The appropriate plan depends on the specific heart abnormality and the cat’s clinical status. Do not start human heart medication, supplements, or over-the-counter treatments without veterinary guidance.
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The outlook varies considerably. A physiologic murmur may have an excellent prognosis. Advanced cardiomyopathy, congestive heart failure, and blood clots are more serious. Cats with HCM can look healthy for a long time, but the disease can progress unpredictably in some individuals.
Common misunderstandings
- “A murmur proves my cat has heart disease.” No. Stress, anemia, fever, low protein, and other conditions can create a murmur.
- “A loud murmur must be the most dangerous.” Not necessarily. Loudness alone cannot determine severity.
- “No murmur means the heart is healthy.” No. Some cats with important heart disease have no detectable murmur.
- “Every kitten murmur is harmless.” No. A murmur that persists, becomes louder, or occurs with poor growth or other signs needs further assessment.
- “Taurine supplements treat most feline heart disease.” This is outdated. Most complete commercial cat foods contain taurine, and most current cardiomyopathy cases are not taurine-responsive. Taurine deficiency is mainly a concern with inappropriate or noncommercial diets and should be investigated with a veterinarian.
What to record before the appointment
- Write down when the murmur was first detected and whether a grade was provided.
- Note changes in appetite, weight, activity, breathing, sleep, or tolerance for play.
- Record your cat’s sleeping respiratory rate on several calm occasions; do not count while purring.
- Bring a list of medications, supplements, flea products, and the cat’s diet.
- If safe, take a short video of unusual breathing or weakness rather than trying to recreate the sign at the clinic.
A murmur deserves follow-up, but it does not automatically mean the worst. The combination of a physical examination, appropriate blood tests, and—when indicated—an echocardiogram can distinguish a harmless flow sound from a condition that needs treatment.
FAQ
Is a heart murmur in a cat always serious?
No. Some murmurs are innocent or caused by temporary changes such as stress, fever, anemia, or low blood protein. Others are linked to congenital defects or heart disease. Testing and monitoring are needed to determine the cause.
Can a kitten outgrow a heart murmur?
Yes. Soft physiologic murmurs can occur during rapid growth, particularly between about 6–8 weeks and 4–5 months, and may disappear. A persistent, loud, or symptom-associated murmur should not be assumed harmless.
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What breathing rate is too high for a cat at rest?
A calm sleeping cat commonly breathes about 15–30 times per minute, according to VCA Animal Hospitals. A persistent rate above 30 should prompt veterinary advice, especially with other signs. Open-mouth breathing or obvious breathing effort is an emergency.
Does a cat with no murmur have a healthy heart?
Not necessarily. Some cats with heart disease, including HCM, have no audible murmur. A murmur is only one physical finding and cannot by itself confirm or exclude heart disease.
The Bottom Line
A heart murmur is a clue, not a diagnosis. It may be harmless, related to a treatable noncardiac illness, or associated with structural heart disease such as HCM. Arrange veterinary follow-up for any newly detected murmur, and seek emergency care for breathing distress, blue or gray gums, collapse, or sudden hind-limb paralysis.
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