Matters of the Heart: Early Detection and New Advances in Feline Heart Disease

With Valentine’s Day arriving, we’re starting to see hearts everywhere we look. They represent the love and affection we feel for our friends, family, and pets. In veterinary medicine, hearts are always on our mind—because heart health deserves attention year-round, especially for cats.

Feline heart disease is common, often silent, and frequently misunderstood. The good news is that modern diagnostics—particularly echocardiography—allow us to identify disease earlier and with greater precision than ever before. And with the recent availability of Felycin-CA1, veterinarians now have the first therapy designed to modify the progression of early-stage hypertrophic cardiomyopathy (HCM) in carefully selected cats.

Understanding what that means begins with understanding how feline heart disease behaves.

Why Heart Disease in Cats Is So Difficult to Detect

The most common form of heart disease in cats is hypertrophic cardiomyopathy (HCM). In HCM, the muscular walls of the heart—particularly the left ventricle—become abnormally thickened. This thickening can interfere with the heart’s ability to relax and fill properly, even when outward signs are absent.

Many cats with HCM:

• Appear completely normal at home

• Have no audible murmur on examination

• Show normal chest radiographs in early stages

In fact, a significant percentage of cats with confirmed HCM do not have a detectable murmur. That means a normal stethoscope exam does not reliably rule out heart disease.

For some cats, the first noticeable sign may be sudden respiratory distress or weakness. That unpredictability is what makes early, accurate diagnosis so important.

Echocardiography: The Gold Standard for Feline Heart Evaluation

An echocardiogram is an ultrasound of the heart. It allows us to see the heart in motion, measure muscle thickness, assess chamber size, and evaluate blood flow patterns in real time. In cats, echocardiography is the only definitive way to diagnose cardiomyopathy and determine its severity.

Other tools are helpful, but limited:

• Listening with a stethoscope is a useful screening tool, but not sensitive enough to rule out disease.

• Chest radiographs are excellent for identifying congestive heart failure, but often appear normal in early HCM.

• Blood tests such as NT-proBNP can help guide decision-making, but they do not define disease type or severity.

Echocardiography provides clarity. It answers essential questions:

• Is heart muscle thickening present?

• How severe is it?

• Is there left atrial enlargement?

• Is there evidence of obstruction or increased risk?

Those details guide monitoring, risk assessment, and long-term planning.

What We Look for on an Echocardiogram

During an echocardiogram, several key parameters are evaluated:

Heart Muscle Thickness

Measurements of the left ventricular walls help determine whether hypertrophy is present. In general, a wall thickness of 6 mm or greater is consistent with HCM, though breed and body size are always considered. The pattern and distribution of thickening also matter.

Heart Function

Many cats with HCM have normal or even increased squeezing function. The challenge often lies in relaxation—how the heart fills between beats. Doppler evaluation also helps detect dynamic outflow obstruction, which can worsen under stress.

Left Atrial Size

Enlargement of the left atrium is one of the most important prognostic indicators. Increased size correlates with higher risk of congestive heart failure and arterial thromboembolism. Identifying changes early allows for closer monitoring and informed medical decisions.

These measurements are not theoretical—they directly influence how we counsel families and collaborate with primary veterinarians.

A Shift in Feline Cardiac Care: Introducing Felycin-CA1

For many years, managing feline HCM meant monitoring cats carefully and treating complications if and when they occurred. Medications were typically introduced after congestive heart failure developed.

In March 2025, that approach evolved.

Felycin-CA1 received conditional FDA approval as the first disease-modifying therapy for feline HCM. It is designed specifically for cats with early-stage disease—those who have structural heart thickening identified on echocardiogram but have not yet developed congestive heart failure.

How Felycin-CA1 Works

Felycin-CA1 contains sirolimus, a medication that targets a pathway in the body known as mTOR. This pathway plays a role in the abnormal thickening of the heart muscle seen in HCM. By inhibiting this pathway, the medication aims to slow or reduce further thickening of the left ventricle.

In the RAPACAT clinical study, cats receiving sirolimus demonstrated a reduction in maximum heart wall thickness compared to placebo-treated cats.

This is a meaningful distinction. Rather than only reacting to heart failure, veterinarians may now consider earlier intervention in carefully selected patients.

Who Is a Candidate for Felycin-CA1?

Echocardiography remains essential.

Felycin-CA1 is indicated for cats with:

• Left ventricular wall thickness of 6 mm or greater

• No clinical signs of congestive heart failure

It does not replace echocardiograms. It does not substitute for emergency heart failure treatment. Instead, it is considered when structural disease is present but the cat is still clinically stable.

The medication is administered orally once weekly at a target dose of 0.3 mg/kg, ideally given with food.

Because sirolimus affects immune regulation, appropriate screening is required prior to initiation. Cats must be evaluated for liver disease, and the medication is not recommended in cats with liver disease or diabetes. As with any long-term therapy, monitoring and communication with your veterinarian are important.

From Reactive to Proactive Heart Care

The availability of Felycin-CA1 allows for a shift in mindset. Instead of waiting for complications to occur, there may be an opportunity—when appropriate—to intervene earlier in the course of disease.

This does not eliminate risk. It does not cure HCM. But in selected patients, it may help influence how the disease progresses over time.

The foundation of that decision is always accurate diagnosis. Echocardiography provides the information needed to determine:

• Whether heart disease is present

• How advanced it is

• Whether early intervention is appropriate

Protecting the Heart You Love

Cats rarely tell us when something is wrong with their hearts. That silence is part of what makes feline heart disease so challenging—and why early detection matters so deeply.

Echocardiography allows us to see what cannot be heard. Felycin-CA1 offers a new option for carefully selected cats with early disease. Together, they represent progress in how we care for feline hearts: informed, thoughtful, and proactive.

If your veterinarian has recommended cardiac evaluation, or if your cat has been diagnosed with heart muscle thickening, an echocardiogram provides clarity. And for some cats, that clarity may open the door to earlier intervention.

Because loving a cat’s heart means protecting it long before it ever shows signs of breaking.