Breed Health Guide • Reviewed by Dr. Tiffany Delacruz, DVM
Hypertrophic Cardiomyopathy (HCM) in Norwegian Forest Cats
Also known as: HCM
Hypertrophic Cardiomyopathy is the most common heart disease in cats, and Norwegian Forest Cats have a documented elevated breed risk. The disease thickens the heart muscle, eventually leading to heart failure, arrhythmias, or aortic thromboembolism (saddle thrombus). Early screening and ongoing cardiology care meaningfully change outcomes.
Why Norwegian Forest Cats are predisposed to hypertrophic cardiomyopathy (hcm)
Genetic. Norwegian Forest Cats, Maine Coons, Ragdolls, British Shorthairs, and Sphynx are all over-represented for HCM. The specific mutations vary by breed; in Norwegian Forest Cats, multiple genetic loci have been investigated. Annual cardiac screening starting young is the standard recommendation for the breed.
What you'll see at home
- Often NONE in the early disease phase
- Increased respiratory rate at rest (>30 in a sleeping cat is concerning)
- Open-mouth breathing or panting at rest
- Lethargy and reduced activity
- Heart murmur or gallop on exam
- Sudden hind limb paralysis with screaming — aortic thromboembolism (saddle thrombus) — EMERGENCY
- Sudden death in some cases
Red flags — go to an emergency vet
- ⚠ Sudden hind limb paralysis or weakness with screaming — SADDLE THROMBUS, DRIVE TO ER
- ⚠ Open-mouth breathing or panting at rest
- ⚠ Severe respiratory distress
- ⚠ Collapse
- ⚠ Cyanotic (blue/gray) gums
How vets diagnose hypertrophic cardiomyopathy (hcm)
Annual cardiac auscultation. Echocardiogram is the gold standard for diagnosis and staging. NT-proBNP blood test is a useful screening tool — if abnormal, echocardiogram. Genetic testing for some breed-specific mutations is available.
Treatment options
Asymptomatic HCM with significant cardiac changes: atenolol historically, increasingly clopidogrel for clot prevention in cats with severe left atrial enlargement. Congestive heart failure: furosemide, ACE inhibitor, sometimes pimobendan (used in cats with care). Saddle thrombus: emergency care, pain management, and unfortunately limited treatment options. Lifelong cardiology follow-up.
Living with a Norwegian Forest Cat who has hypertrophic cardiomyopathy (hcm)
- 1 Annual cardiac auscultation by your vet from young adulthood
- 2 Echocardiogram if any murmur or gallop is heard
- 3 Count resting respiratory rate at home — >30 in a sleeping cat warrants vet contact
- 4 Clopidogrel for cats with significant left atrial enlargement to prevent thromboembolism
- 5 Lifelong cardiology follow-up for confirmed HCM
- 6 Avoid IV fluid overload in known HCM cats during any procedure
- 7 Discuss with breeders: Norwegian Forest Cat breeding stock should be HCM-screened
- 8 Pet insurance for cardiac conditions is meaningful — buy young
Can RexVet help with this online?
RexVet is well-suited for: refilling established cardiac medications, coaching on home respiratory rate monitoring, explaining echocardiogram results and disease staging, and quality-of-life conversations.
Start a $64.99 video visit →We cannot perform cardiac auscultation, echocardiograms, or chest radiographs by video. Initial HCM diagnosis and ongoing cardiology care belong with a veterinary cardiologist. Saddle thrombus is a true emergency requiring immediate in-person care.
Prognosis — what to expect
Variable. Mild asymptomatic HCM may not significantly affect life span. Moderate to severe HCM, particularly with significant atrial enlargement, carries risk of CHF and thromboembolism. Median survival once symptomatic is typically 1-2 years with treatment. Saddle thrombus is often catastrophic.
Frequently asked questions
Frequently asked questions
When should my Norwegian Forest Cat be screened for HCM?
Annual cardiac auscultation from young adulthood. Echocardiogram is recommended at age 1-2 in the breed even without a murmur, then repeat as your cardiologist recommends. Many HCM cats have no murmur in early disease.
Can HCM be cured?
No — the disease is progressive. Treatment slows progression, manages CHF when it develops, and prevents thromboembolism. The goal is delay and quality of life rather than cure. Some cats with mild HCM never develop clinical signs.
What is saddle thrombus and how do I recognize it?
Saddle thrombus is a blood clot that lodges where the aorta divides at the back legs. It causes sudden hind limb paralysis or severe weakness, often with screaming pain, cold and pulseless back legs, and blue paw pads. It's a true emergency — drive to the ER immediately. Outcomes are often poor but immediate care offers the only chance.
Further reading from the RexVet blog
Other helpful RexVet resources for Norwegian Forest Cats parents
Sources
- American College of Veterinary Internal Medicine — Cardiology
- Cornell Feline Health Center — Cardiomyopathy
- TICA Norwegian Forest Cat Breed Profile
Last fact-checked: 2026-06-04. Reviewed by Dr. Tiffany Delacruz, DVM.
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