Changing the Story of Feline Heart Disease

Early detection and a new treatment option may shift the course of HCM in cats

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats and also one of the most difficult to detect without expensive heart imaging. Most cats with HCM look perfectly healthy. They eat well, play normally, and show no obvious signs of illness. Even a heart murmur, if present, is not a definitive clue. According to the 2020 ACVIM Consensus Statement, murmurs can be heard in both healthy cats and those with heart disease. In fact, many cats with HCM have no murmur at all. Finally, in some, the first sign of heart disease is sudden death or serious complications caused by abnormal blood clot formation.

That makes early detection both essential and challenging. Echocardiography remains the gold standard for diagnosis, and proactive screening is recommended for at-risk cats. This includes cats with murmurs or gallop sounds, and breeds like Maine Coons and Ragdolls that are more likely to develop heart disease. However,HCM often affects cats without a known pedigree and can develop quietly, with no outward signs—making early detection more important than many we’ve historically recognized.

Until recently, no treatment had been proven to slow or reverse HCM in its early, symptom-free stage. But that may be about to change.

New Research, New Hope: The RAPACAT Trial

A promising new study, the RAPACAT trial (Kaplan et al., 2023), has introduced a potential breakthrough: once-weekly delayed-release (DR) rapamycin. In this multicenter, placebo-controlled study, 43 cats with subclinical HCM were followed for six months to measure changes in heart muscle thickness.

The results were encouraging. Cats treated with DR rapamycin had a significant reduction in left ventricular wall thickness, a key marker of disease progression, compared to those given a placebo. Importantly, the treatment was well tolerated with no significant increase in adverse effects.

This may be the first disease-modifying therapy for cats with HCM before symptoms develop.

Early Detection is More Important Than Ever

The availability of Felycin-CA®, a once-weekly medication for cats with early-stage HCM, marks a turning point in feline heart care. But to treat early, we need to identify disease early. That is where new diagnostic tools are making a difference.

MicroRNA-based tests are especially promising. These molecular biomarkers may help detect disease before clinical signs appear. Earlier diagnosis allows veterinarians to start treatment sooner and have timely conversations with pet owners about managing the condition. For more information, please visit our poster from this year’s ACVIM Forum.

What This Means for Your Patients

The availability of a once-weekly therapy for subclinical HCM, combined with the potential of microRNA-based diagnostics, represents a significant step forward in feline cardiology. As new tools emerge, the opportunity to detect HCM before clinical signs appear is becoming more achievable.

This shift from reactive to proactive care underscores the importance of regular cardiac screening in cats. Earlier detection enables earlier intervention, improved monitoring, and more meaningful conversations with clients about disease trajectory and management.

By incorporating emerging diagnostics and therapies into your clinical approach, you can help change the outcome for cats with HCM, starting before the clinical signs appear.

References:

Fuentes VL, Abbott J, Chetboul V, Côté E, Fox PR, Häggström J, Kittleson MD, Schober K, Stern JA. ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. J Vet Intern Med 2020;34:1062–77. https://doi.org/10.1111/jvim.15745.

Kaplan JL, Rivas VN, Walker AL, Grubb L, Farrell A, Fitzgerald S, Kennedy S, Jauregui CE, Crofton AE, McLaughlin C, Zile RV, DeFrancesco TC, Meurs KM, Stern JA. Delayed-release rapamycin halts progression of left ventricular hypertrophy in subclinical feline hypertrophic cardiomyopathy: results of the RAPACAT trial. J Am Vet Méd Assoc 2023;261:1–10. https://doi.org/10.2460/javma.23.04.0187.

Felycin®-CA1 (sirolimus delayed-release tablets) Redefines Feline Cardiac Care [Internet]. [cited 2025 Jul 6]. Available from:

Hanks E, Coultous R, Capewell P, Palarea-Albaladejo J, Dukes-McEwan J. Application of a Novel MicroRNA Platform to Cardiac Disease Diagnoses in Companion Animals. Poster presented at American College of Veterinary Internal Medicine (ACVIM) Forum; June 19-21, 2025; Louisville, Kentucky.