🐾 Vet’s 2025 Guide to Feline Hypertrophic Cardiomyopathy (HCM)

By Dr Duncan Houston BVSc – Explore causes, symptoms, diagnostics, treatment options—including exciting new therapy—and how to support cats living with HCM. 🐱❤️

📌 Table of Contents

1. What Is HCM?
2. Causes & Predispositions
3. Signs & When to Be Concerned
4. How Veterinarians Diagnose HCM
5. Traditional Treatment Options
6. Sirolimus: A New Hope for Cats
7. Monitoring & Home Care
8. Managing Complications
9. Quality of Life & Prognosis
10. Ask A Vet, Woopf & Purrz Support
11. Summary & Care Checklist

1. What Is HCM?

Hypertrophic cardiomyopathy (HCM) is the most common heart condition in cats. It involves abnormal thickening of the left ventricle’s muscular walls, which reduces chamber space and stiffens the heart. This leads to reduced blood flow, diastolic dysfunction, and risks such as heart failure, blood clots, or sudden death :contentReference[oaicite:3]{index=3}.

As HCM progresses, it narrows the left ventricular outflow tract (LVOT), sometimes causing the mitral valve to flap into the chamber — a condition known as systolic anterior motion (SAM) — which further obstructs blood flow :contentReference[oaicite:4]{index=4}.

2. Causes & Predispositions

• Genetic mutations: Common in breeds like Maine Coons, Ragdolls, Persians, Sphynx; A31P (Maine Coon) and other sarcomeric gene mutations have been identified :contentReference[oaicite:5]{index=5}.
• Idiopathic cases: No identifiable cause in many cats :contentReference[oaicite:6]{index=6}.
• Secondary thickening: Caused by hyperthyroidism or high blood pressure, which must be ruled out :contentReference[oaicite:7]{index=7}.

3. Signs & When to Be Concerned

Many cats with HCM are asymptomatic until later stages. Signs can include:

• Labored breathing, rapid respiratory rate, or open-mouth breathing :contentReference[oaicite:8]{index=8}.
• Lethargy, decreased appetite, coughing less common :contentReference[oaicite:9]{index=9}.
• Heart murmur or gallop rhythm; however, some cats have no audible murmur :contentReference[oaicite:10]{index=10}.
• Aortic thromboembolism (“saddle thrombus”)—sudden hind limb paralysis and severe pain :contentReference[oaicite:11]{index=11}.
• Fainting, collapse, or sudden death in advanced cases :contentReference[oaicite:12]{index=12}.

4. How Veterinarians Diagnose HCM

• Physical exam: Listening for murmurs or abnormal sounds.
• Chest radiographs: Assess heart size and check for pleural effusion :contentReference[oaicite:13]{index=13}.
• Echocardiography: The gold standard—visualizes wall thickening, SAM, chamber sizes :contentReference[oaicite:14]{index=14}.
• Blood biomarkers: NT‑proBNP helps detect subclinical disease :contentReference[oaicite:15]{index=15}.
• Other tests: Blood pressure, thyroid levels, ECG to check for arrhythmias :contentReference[oaicite:16]{index=16}.

5. Traditional Treatment Options

Although there is no cure, treatment aims to manage symptoms:

• Beta blockers (atenolol): Slow heart rate, reduce LVOT obstruction :contentReference[oaicite:17]{index=17}.
• ACE inhibitors (benazepril): Lower blood pressure and ease heart workload, typically used in heart failure :contentReference[oaicite:18]{index=18}.
• Diuretics (furosemide, spironolactone): Reduce fluid buildup in lungs and chest :contentReference[oaicite:19]{index=19}.
• Pimobendan: Improves heart contraction and blood flow :contentReference[oaicite:20]{index=20}.
• Clopidogrel (Plavix): Reduces risk of thromboembolism; preferred over aspirin :contentReference[oaicite:21]{index=21}.
• Nitroglycerin ointment: Ears-applied vasodilator in acute fluid buildup :contentReference[oaicite:22]{index=22}.
• Oxygen therapy, sedation, pleurocentesis: Supportive emergency care for advanced cases :contentReference[oaicite:23]{index=23}.

6. Sirolimus: A New Hope for Cats

In March 2025, the FDA granted conditional approval for Felycin‑CA1 (sirolimus) to manage subclinical HCM. Clinical trials show it may reverse ventricular thickening and improve prognosis :contentReference[oaicite:24]{index=24}.

This marks a milestone: the first medication aiming to treat the disease biologically, not just its symptoms. Further studies are ongoing to confirm long-term benefits :contentReference[oaicite:25]{index=25}.

7. Monitoring & Home Care

• Resting respiratory rate: Should stay under ~36 bpm; sustained increase means vet visit :contentReference[oaicite:26]{index=26}.
• Regular checkups: Asymptomatic cats: echo yearly; symptomatic or CHF: every 3–6 months :contentReference[oaicite:27]{index=27}.
• Stress reduction: Calm environment supports breathing and heart health :contentReference[oaicite:28]{index=28}.
• Diet & supplements: Low‑sodium diet with high‑quality protein, omega‑3s, and B vitamins may aid appetite and health :contentReference[oaicite:29]{index=29}.
• Track weight & activity: Daily logs help detect early decline.

8. Managing Complications

• Aortic thromboembolism: Severe leg pain, cold limbs—urgent care; treatment includes pain control and supportive care :contentReference[oaicite:30]{index=30}.
• Congestive heart failure: Repeated pleurocentesis, oxygen support, medication optimization :contentReference[oaicite:31]{index=31}.
• Arrhythmias: ECG or Holter monitoring identifies abnormal rhythms treated with antiarrhythmic drugs :contentReference[oaicite:32]{index=32}.

9. Quality of Life & Prognosis

Prognosis varies widely: asymptomatic cats may live normal lifespans, while those with CHF have median survival ~12 months, and those developing clots often have shorter spans :contentReference[oaicite:33]{index=33}.

Early detection and thoughtful management—including the new sirolimus therapy—can significantly improve outcomes and comfort :contentReference[oaicite:34]{index=34}.

10. Ask A Vet, Woopf & Purrz Support 💬

Need personalized advice on diagnostics, treatment, or lifestyle adjustments? Reach out to Ask A Vet anytime. Use Woopf low‑stress feeding tools and calming Purrz lounges to help reduce stress and support ongoing care for cats with heart concerns. 🐾

11. Summary & Care Checklist ✅

• ✔️ HCM = thickened heart; no cure but manageable.
• ✔️ Diagnose via echo, X‑rays, biomarkers, ECG.
• ✔️ Medications: atenolol, benazepril, diuretics, pimobendan, clopidogrel.
• ✔️ Sirolimus (Felycin‑CA1) offers potential disease modification.
• ✔️ Monitor RRR, weight, stress, recheck echo 1–2× yearly.
• ✔️ Emergency signs: difficulty breathing, sudden paralysis → vet visit immediately.
• ✔️ Consult Ask A Vet; use Woopf & Purrz to support cardiac comfort.

With early detection, compassionate care, and the latest therapies, cats with HCM can enjoy meaningful, comfortable lives. Stay proactive, stay informed, and let veterinary support—like Ask A Vet—guide your journey together. ❤️