Breed Health Guide • Reviewed by Dr. Tiffany Delacruz, DVM
Hypertrophic Cardiomyopathy in British Shorthairs
Also known as: HCM
British Shorthairs have an elevated risk of Hypertrophic Cardiomyopathy (HCM) compared to the general cat population. Unlike Maine Coons and Ragdolls — which have well-characterized single-gene mutations — the genetic basis of HCM in British Shorthairs is less well understood, with multiple suspected susceptibility variants and no commercial single-mutation test available.
Why British Shorthairs are predisposed to hypertrophic cardiomyopathy
British Shorthairs are over-represented in published HCM case series, but the breed lacks the single-mutation genetic test available for Maine Coons and Ragdolls. Research suggests polygenic inheritance with multiple as-yet-uncharacterized variants. Selective breeding within a relatively small founder population may have concentrated cardiac susceptibility alleles. Because no genetic test is available, echo screening is the only practical surveillance tool.
What you'll see at home
- Often nothing visible — HCM is silent in pre-clinical phases
- Heart murmur on routine vet exam (when present)
- Reduced activity, hiding, lethargy
- Increased resting respiratory rate while sleeping (>30/min)
- Open-mouth breathing or visible respiratory effort
- Sudden hind-leg paralysis or screaming (aortic thromboembolism — saddle thrombus)
- Collapse or fainting
- Sudden cardiac death (sometimes the first sign)
Red flags — go to an emergency vet
- ⚠ Open-mouth breathing (cats rarely pant — true emergency)
- ⚠ Sudden hind-leg paralysis (aortic thromboembolism)
- ⚠ Sleeping respiratory rate over 40/min
- ⚠ Collapse, fainting, or severe lethargy
- ⚠ Pale, blue, or grey gums
How vets diagnose hypertrophic cardiomyopathy
Annual cardiac auscultation. Echocardiography by a cardiologist is the gold standard and the only definitive way to confirm HCM in British Shorthairs in the absence of a genetic test. NT-proBNP blood test can screen for cardiac muscle stress.
Treatment options
Pre-clinical with no atrial enlargement — monitor only. Pre-clinical with atrial enlargement — atenolol and/or clopidogrel. Clinical heart failure — multi-drug therapy: furosemide, pimobendan, ACE inhibitor, clopidogrel. Saddle thrombus is treated emergently with pain control and supportive care.
Common medications for this condition
Don't start, stop, or change any of these medications without a licensed vet's guidance.
Living with a British Shorthair who has hypertrophic cardiomyopathy
- 1 Cardiac auscultation at every annual vet exam
- 2 Echo screening at age 1, then every 1-2 years
- 3 Sleeping respiratory rate at home — weekly check
- 4 Lean body weight, indoor only, low stress
- 5 Strict adherence to cardiac medications
- 6 Know your 24/7 ER vet — saddle thrombus is sudden
- 7 Avoid breeding cats with confirmed HCM
Can RexVet help with this online?
RexVet is well-suited for atenolol, clopidogrel, furosemide, pimobendan refills, respiratory rate monitoring, side-effect management, and triaging new symptoms.
Start a $64.99 video visit →We can't perform echocardiograms, chest x-rays, or genetic tests by video. Acute decompensation needs an ER vet.
Prognosis — what to expect
Pre-clinical British Shorthairs often live full lifespans with monitoring. Clinical heart failure cases have a median survival of 12-18 months with treatment. Saddle thrombus is typically devastating. Early detection through echo screening is the most important lever.
Frequently asked questions
Frequently asked questions
Is there a genetic test for HCM in British Shorthairs?
Not currently. Unlike Maine Coons (MyBPC3 A31P) and Ragdolls (MyBPC3 R820W), no single causal mutation has been identified in British Shorthairs for which a commercial test exists. Echo screening from age 1+ is the only practical surveillance tool.
At what age does HCM show up in British Shorthairs?
Variable — some cats have detectable changes on echo as young as 1-2 years, others not until middle age or later. Annual echo screening from age 1 is recommended for breeding cats and for any British Shorthair you want monitored. Most cats with HCM are diagnosed at routine screening before symptoms develop.
Can a British Shorthair with HCM live a normal life?
Many do. Pre-clinical cases (HCM on echo but no left atrial enlargement) often need only monitoring. As atrial enlargement develops, preventive medications are added. The cats who do poorly are those who present in clinical heart failure or with saddle thrombus — outcomes for those are more guarded. Early screening tilts the odds dramatically.
Should I screen my British Shorthair if it's not used for breeding?
Yes — even pet British Shorthairs benefit from early echo screening. Catching HCM in the pre-clinical phase allows for medication that may delay or prevent heart failure and reduce thromboembolism risk. The screening is non-invasive and most cats tolerate echo without sedation.
Sources
Last fact-checked: 2026-06-01. Reviewed by Dr. Tiffany Delacruz, DVM.
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