British Shorthairs are one of the breeds in which hypertrophic cardiomyopathy (HCM) is seen more often than average, and genetics appear to play a role in at least some affected lines, though the specific mutations responsible have not been identified in this breed as they have in Maine Coons and Ragdolls. The single most important thing an owner should know is that HCM is often silent in its early stages, so regular veterinary check-ups (including listening for heart murmurs or arrhythmias) and prompt attention to any change in breathing, energy or appetite give your cat the best chance of early detection and management.
Why British Shorthairs Are Prone to HCM
Hypertrophic cardiomyopathy is the most commonly diagnosed heart disease in cats generally, but certain breeds, including the British Shorthair, Maine Coon, Ragdoll and Sphynx, are recognised as being over-represented in cases seen by vets and cardiologists. In British Shorthairs, this predisposition is believed to be at least partly inherited, meaning it can run in certain bloodlines and be passed from parent to kitten. Unlike in Maine Coons, where a specific genetic mutation has been identified and can be tested for, no single gene has been confirmed as the cause in British Shorthairs, so genetic testing cannot reliably tell you whether an individual cat is affected or a carrier.
HCM causes the walls of the heart's main pumping chamber (the left ventricle) to thicken abnormally. This thickening makes the heart less efficient at relaxing and filling with blood between beats, which can eventually lead to reduced blood flow, fluid build-up in or around the lungs, and in some cases dangerous blood clots. Because British Shorthairs are a naturally solid, muscular breed, some owners and even vets can find early heart changes harder to spot on a physical exam alone, which makes routine screening particularly valuable in this breed. If you're considering the breed or already share your home with one, it's worth reading the British Shorthair breed guide for a fuller picture of their health profile alongside this condition.
Early Signs and Symptoms to Watch
One of the most challenging aspects of HCM is that many cats show no obvious symptoms until the disease is quite advanced. This is why it's sometimes called a "silent" disease. However, attentive owners may notice subtle changes over time, including:
- Breathing that seems faster or more laboured than usual, even at rest
- Reduced activity, tiring more easily during play, or reluctance to jump
- Hiding more than usual or general quietness
- Reduced appetite or subtle weight loss
- Open-mouth breathing (this is never normal in a resting cat)
- A heart murmur, irregular heart rhythm, or gallop sound detected by your vet during a routine check-up
Because cats are experts at masking illness, many of these signs are easy to miss or attribute to ageing or a "lazy" temperament, especially in a breed already known for being calm and low-energy. Regular veterinary examinations give your vet the chance to pick up murmurs or rhythm abnormalities before you notice anything at home.
When It's an Emergency
Some cats with HCM remain stable for years, while others can deteriorate suddenly. Certain signs indicate a genuine emergency and require immediate veterinary attention, ideally at an emergency clinic if your own vet is unavailable:
- Open-mouth or laboured breathing, or breathing with an exaggerated abdominal effort
- Sudden collapse or extreme lethargy
- A sudden onset of weakness or paralysis in the back legs, sometimes with pain or crying out (this can indicate a blood clot, known as feline aortic thromboembolism, a well-recognised and serious complication of HCM)
- Pale, grey or bluish gums
- Sudden loss of appetite combined with hiding and reduced responsiveness
These signs can indicate congestive heart failure or a thromboembolic event, both of which are life-threatening and time-critical. Do not wait to see if things improve; earlier veterinary intervention gives the best chance of stabilising your cat.
How HCM Is Diagnosed
Diagnosis typically begins with a thorough physical examination, where your vet will listen carefully for heart murmurs, gallop rhythms or irregular heartbeats. However, it's important to know that some cats with significant HCM have no audible murmur at all, and some murmurs are unrelated to HCM, so listening alone cannot confirm or rule out the disease.
If HCM is suspected, further tests are usually recommended, which may include:
- Echocardiogram (heart ultrasound) — the gold-standard test, allowing a vet or veterinary cardiologist to directly measure the thickness of the heart walls and assess how well the heart is functioning
- Chest X-rays — useful for checking for fluid in or around the lungs if heart failure is suspected
- Blood tests, including a biomarker called NT-proBNP, which can be elevated when the heart is under strain (though this is a supporting tool, not a definitive diagnostic test on its own)
- Blood pressure measurement and thyroid testing, since high blood pressure and hyperthyroidism can cause heart thickening that mimics or worsens HCM, and need to be ruled out or addressed
Many vets recommend periodic cardiac screening for at-risk breeds, particularly before breeding, before anaesthesia for routine procedures like neutering, and as part of general senior health checks.
Management and Treatment Options
There is no cure for HCM, but there is a great deal that can be done to manage the condition, slow progression of symptoms, and maintain quality of life. Treatment is tailored to the individual cat and the stage of disease, and may include:
- Medications to help the heart relax and fill more efficiently, control heart rate or rhythm, or reduce the workload on the heart
- Diuretics if fluid has built up in or around the lungs, to help remove excess fluid
- Anti-clotting medication for cats at risk of thromboembolism, particularly those with an enlarged left atrium (the heart chamber most associated with clot formation)
- Regular monitoring via repeat echocardiograms to track how the disease is progressing and adjust treatment accordingly
- Addressing underlying or contributing conditions, such as hyperthyroidism or high blood pressure, if present
Cats with mild HCM and no symptoms may not need medication straight away but will benefit from ongoing monitoring. Cats with more advanced disease or a history of heart failure will usually need lifelong medication and closer follow-up with your vet or a veterinary cardiologist.
Prevention and Daily Care
Because the exact genetic cause in British Shorthairs isn't fully understood, there's no guaranteed way to prevent HCM. However, responsible steps can reduce risk and support early detection:
- Choose a breeder who screens their breeding cats for heart disease, ideally with regular echocardiograms performed by a suitably experienced vet
- Avoid breeding from cats diagnosed with HCM or from lines with a known history of the disease
- Book routine veterinary check-ups, and mention if you notice any change in your cat's breathing, energy or behaviour, however subtle
- Keep your cat at a healthy weight, as obesity puts additional strain on the heart
- Avoid unnecessary stress and ensure any anaesthetic procedures are preceded by appropriate pre-anaesthetic screening, particularly for middle-aged and older cats
Cost and Prognosis Realism
It's worth being honest with yourself about the practical side of HCM. Diagnostic work-ups involving echocardiography and specialist cardiology input are not inexpensive, and ongoing management often involves lifelong medication, repeat scans and regular vet visits. Costs can add up significantly over a cat's lifetime, so pet insurance taken out while your cat is young and healthy (before any heart changes are detected) can make a real difference to your options later on.
Prognosis varies enormously between individual cats. Some live for many years with mild, stable HCM and minimal intervention, while others progress to heart failure or suffer a thromboembolic event, both of which carry a more guarded outlook. Regular monitoring genuinely does improve outcomes, as it allows treatment to be started or adjusted before a crisis occurs, rather than after one.
Frequently Asked Questions
Can kittens be tested for HCM before I bring one home?
An echocardiogram can be performed on a kitten, but because HCM often develops later in life, a clear scan in a young kitten doesn't guarantee the cat won't develop the disease as an adult. Ask breeders about the cardiac screening history of both parents rather than relying solely on kitten testing.
Is my British Shorthair definitely going to get HCM?
No. Being a predisposed breed means the risk is higher than average, not that every British Shorthair will develop the condition. Many live long, healthy lives with no heart problems at all, particularly those from well-screened lines.
How often should my cat's heart be checked?
This depends on age, breed and individual risk factors, so it's best discussed with your vet. Many vets recommend a baseline check in young adulthood, with periodic re-checks as your cat ages, and prompt evaluation any time new symptoms appear.
This article is for general informational purposes only and is not a substitute for professional veterinary advice. Please consult your vet for accurate diagnosis and treatment of your cat's individual condition.