Early Signs of Heart Disease in Cats — and the Ones That Are Emergencies

Short answer: most cats with heart disease show nothing at all until the disease is advanced — no cough, no exercise intolerance you would notice in an indoor animal, often not even a murmur. The early signs that do exist are quiet: faster resting breathing, sleeping more, subtle withdrawal. The single most useful thing an owner can do at home is count the sleeping respiratory rate — and know the three presentations that mean an emergency room, not an appointment.

Why cats are different

Dogs with heart disease cough, tire on walks, and announce themselves. Cats do neither. They do not exercise on command, so nobody notices reduced stamina; they rarely cough from heart disease; and they are evolutionary experts at concealing weakness. The most common feline heart disease — hypertrophic cardiomyopathy — is routinely discovered either incidentally or at the moment of crisis.

That asymmetry is the core fact of feline cardiology: absence of signs is not absence of disease.

The early signs worth taking seriously

• Faster breathing at rest. The most important one, and the most measurable — see below.
• Sleeping more, engaging less. Not dramatic lethargy; a quiet shrinking of activity that is easy to attribute to age.
• Reduced grooming, a coat that looks slightly neglected.
• Hiding more, or a change in where the cat chooses to rest.
• Open-mouth breathing after play or stress — never normal in a cat.
• A newly noticed murmur or gallop rhythm at a routine visit — a sound, not a diagnosis, but a workup trigger. We covered what murmurs do and do not mean in our murmur guide.

None of these is specific to the heart. All of them are reasons for a veterinary visit, where NT-proBNP testing and echocardiography can settle the question properly.

The one number to track at home

Count your cat's breaths while it sleeps — one rise and fall of the chest is one breath. Do it for 30 seconds and double it. A healthy sleeping rate is usually under 30 breaths per minute. A persistent rate above 30, or a clear upward trend across days, is among the earliest detectable signs of congestive heart failure — often visible at home a week or more before a crisis.

It costs nothing, takes half a minute, and for cats with a known murmur or diagnosed HCM it should be a weekly habit.

The three emergencies

Go now — not tomorrow — if you see:

1. Laboured or open-mouth breathing at rest. Fluid around or in the lungs. Minutes-to-hours matters.
2. Sudden hind-leg weakness or paralysis, with pain and cold paws. A clot (arterial thromboembolism) blocking blood flow — the most painful emergency in feline medicine.
3. Collapse or fainting.

All three are treatable enough that speed changes outcomes, and none improves with waiting.

After the diagnosis

If a workup finds heart disease, the case belongs with your veterinarian and, ideally, a veterinary cardiologist. For the most common diagnosis — subclinical HCM — monitoring is the backbone, and it is also the stage where progression-slowing is now an evidence-backed research area rather than a hope; the honest state of that evidence is in our HCM guide.

The summary an owner can act on: watch the quiet signs, count the sleeping breaths, and treat the three emergencies as emergencies. In feline heart disease, the owner who notices early is the intervention.