My cat has a murmur but seems perfectly well: should I worry?

A murmur is just a sound that indicates turbulent blood flow and does not equal disease. Many cats with a murmur have a normal heart and some cats with HCM have no murmur at all. The right way to answer the question is an echocardiogram, which actually measures wall thickness and heart function. If it is normal, the vet will tell you whether and when to repeat it, based on breed and age.

How do I count the resting breathing rate at home?

Wait until the cat is asleep or resting quietly, not right after play or in a warm room. Watch the chest and count one breath for each full cycle, in and out, over fifteen seconds, then multiply by four. A steady value below 30 breaths per minute is reassuring. Log the number: it is the trend over time, more than the single value, that flags a problem on the way.

There is no cure that returns the thickened muscle to normal, but there are treatments that manage complications, slow heart failure and reduce clot risk. The aim is to preserve quality of life for as long as possible. The plan depends on the stage of disease and the echocardiogram findings, and it should be followed consistently even during periods when the cat appears perfectly well.

Does diet affect hypertrophic cardiomyopathy?

Unlike some forms linked to taurine deficiency, classic feline HCM is not caused by diet and is not corrected by a particular food. A complete, balanced diet still matters for weight and general health, and in heart failure the vet may advise adjustments to sodium or fluid intake. Avoid do it yourself cardiac supplements, because they do not replace treatment and may interfere.

Health and prevention8 min readUpdated on August 20, 2026

Feline hypertrophic cardiomyopathy: recognising a silent disease

Hypertrophic cardiomyopathy is the most common feline heart disease and stays silent for a long time: early signs, useful tests and how to live with the diagnosis.

Audience: Pet owners
Species: Cat
Scope: Valid everywhere, European Union, Italy

Hypertrophic cardiomyopathy, or HCM, is the most common heart disease in cats and also one of the hardest to catch in time, because for years it produces no obvious symptom. The wall of the left ventricle thickens, the chamber shrinks and the heart struggles to fill properly, yet the cat keeps eating, playing and behaving normally. Many owners only discover the diagnosis on the day their cat has a sudden breathing crisis or an acute paralysis of a leg, when the disease has in fact been present for a long time. Understanding how this condition works in silence, which household signs can flag trouble early and which tests allow you to act before a crisis makes a real difference to the quality and length of a cat's life. This page lays out the useful ideas without replacing a cardiology consultation.

Why it stays hidden for so long

A cat masks illness by instinct and moves far less than a dog. A heart that pumps less well is compensated simply by reducing activity: the cat sleeps more, jumps a little lower, tires sooner, and these changes get blamed on age or personality. There is no exertional cough like the one seen in cardiac dogs, so the alarm bell that pushes many dog owners to book a visit is missing.

HCM also has a strong inherited component in some breeds, including the Maine Coon, Ragdoll, British Shorthair and Sphynx, but it affects the ordinary non pedigree cat too. It can appear in a young adult or develop with the years, and its severity varies widely: some cats live with a mild form all their lives, while others progress to heart failure within months.

Early signs and late signs

Do not expect a single symptom. It helps to separate the small changes that warrant a scheduled visit from the signs that demand the clinic the same day or straight away.

How to read the changes by urgency
Observation	What it may indicate	What to do
Sleeps more, plays less, tires sooner	Reduced cardiac reserve, often the first sign	Note it and request a scheduled visit
Resting breathing rate above 30 breaths per minute	Early fluid build up in the lungs	Repeat the count and contact the vet
Open mouth breathing, heaving belly, fast laboured breathing	Pulmonary oedema or effusion, active heart failure	Emergency: clinic now, minimal handling
Hind leg suddenly cold, painful, dragged	Arterial thromboembolism, a clot blocking circulation	Immediate emergency, intense pain, do not wait
Fainting or collapse during a moment of excitement	Arrhythmia or outflow obstruction	Urgent cardiology visit

Counting the resting breathing rate, meaning while the cat sleeps peacefully, is the single most useful home tool for this disease. A steady value below 30 breaths per minute is reassuring, whereas a rising trend over a few days often precedes heart failure before breathing becomes visibly laboured.

How the diagnosis is reached

The diagnosis comes not from a single test but from a pathway, which the vet tailors to the individual cat, its age, its breed and any signs already present.

Examination and listening to the heart
The vet listens for a murmur, a gallop rhythm and arrhythmias, checks the pulse and breathing and takes the cat's history. It is the first filter, not the conclusion.
Targeted blood work
A specific cardiac marker plus a thyroid check help separate a struggling heart from other causes. Hyperthyroidism and high blood pressure can thicken the muscle and must be ruled out.
Blood pressure
Measuring blood pressure rules out hypertension that mimics or worsens the picture. It is a quick, low stress test when done calmly.
Echocardiography
This is the test that confirms the diagnosis: it measures wall thickness, the size of the left atrium and any sluggish blood flow that favours clots. It also shows how severe the form is.
ECG and radiographs when needed
These are added if there are arrhythmias to characterise or suspected fluid in the lungs to confirm. They are not always necessary.

Living with the diagnosis

A diagnosis of HCM does not mean the cat is about to become unwell. Many cats live long and well, provided monitoring is consistent and any prescribed treatment is followed precisely.

Measure the resting breathing rate two or three times a week and log the value: it is the figure the vet uses to judge whether compensation is holding.
Give prescribed medication at the set times and never stop it on your own: many cardiac treatments only work if kept constant.
Keep an eye on weight and appetite, because a decline can flag a worsening or an effect of the disease.
Reduce needless stress, avoid excessive heat and keep a predictable environment: crises are often triggered by strong excitement.
Schedule the cardiology follow ups and complete them even when the cat seems in perfect shape.
Report any episode of laboured breathing, marked lethargy or leg pain at once, without putting it off to the next day.

The two emergencies to know

Anyone living with a cardiac cat must recognise two situations that allow no delay, because the useful window is measured in minutes and hours.

Respiratory failure: the cat breathes with its mouth open, the belly heaving, the breath fast and shallow, often refusing to lie down. This is fluid building up in the chest and must be handled at the clinic with the least handling possible.
Arterial thromboembolism: a clot leaving the heart suddenly blocks circulation, usually to the hind legs. Intense pain, a cold and paralysed limb, vocalising and laboured breathing appear. It is one of the most painful emergencies there is and needs immediate care.

Prevention, checks and responsible choices

You cannot stop a predisposed cat from developing HCM, but you can catch it early and lengthen the window of good quality of life. Prevention here means, above all, intelligent surveillance.

In at risk breeds, ask about available genetic tests and the cardiac health of the breeding cats before choosing a kitten.
Include heart auscultation and blood pressure in periodic checks, especially after seven years of age.
Learn to count the resting breathing rate while the cat is well, so you have a personal reference value.
Do not give supplements or fluids on your own: in a diseased heart the wrong fluid load can trigger heart failure.
Report to the vet any change in energy, breathing or appetite, even if it seems trivial.

HCM is a disease many cats live with for years. The difference between a late emergency diagnosis and calm management often comes down to a few observation habits, repeated over time and recorded in an orderly way.

Frequently asked questions

My cat has a murmur but seems perfectly well: should I worry?: A murmur is just a sound that indicates turbulent blood flow and does not equal disease. Many cats with a murmur have a normal heart and some cats with HCM have no murmur at all. The right way to answer the question is an echocardiogram, which actually measures wall thickness and heart function. If it is normal, the vet will tell you whether and when to repeat it, based on breed and age.
How do I count the resting breathing rate at home?: Wait until the cat is asleep or resting quietly, not right after play or in a warm room. Watch the chest and count one breath for each full cycle, in and out, over fifteen seconds, then multiply by four. A steady value below 30 breaths per minute is reassuring. Log the number: it is the trend over time, more than the single value, that flags a problem on the way.
Can HCM be cured?: There is no cure that returns the thickened muscle to normal, but there are treatments that manage complications, slow heart failure and reduce clot risk. The aim is to preserve quality of life for as long as possible. The plan depends on the stage of disease and the echocardiogram findings, and it should be followed consistently even during periods when the cat appears perfectly well.
Does diet affect hypertrophic cardiomyopathy?: Unlike some forms linked to taurine deficiency, classic feline HCM is not caused by diet and is not corrected by a particular food. A complete, balanced diet still matters for weight and general health, and in heart failure the vet may advise adjustments to sodium or fluid intake. Avoid do it yourself cardiac supplements, because they do not replace treatment and may interfere.

What to do next

Hypertrophic cardiomyopathy is the most common feline heart disease and works in silence: learn to count the resting breathing rate while your cat is well, ask for auscultation and blood pressure at checks and an echocardiogram if doubts arise. Recognise the two emergencies, open mouth breathing and a cold, painful leg, and in that case go to the clinic at once with minimal handling. With steady monitoring and treatment followed precisely, many cats live long and well.