The honest starting point
Most of what we write on PAWai is about things you can learn to notice at home: a change in the litter tray, a new limp, a different kind of breathing noise. This post is different, and that's the point of it.
Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. In its early, "preclinical" stage, the cat looks completely well. There is no reliable sign an owner can watch for. It is usually found because a veterinarian hears a murmur or an extra heart sound (a "gallop") during a routine exam, and then confirms it with an ultrasound of the heart (an echocardiogram).
So you can't screen for this at home, and you don't need to feel guilty for not noticing it. What you can do is know the two emergencies it can cause, and keep the record that helps your vet follow it over the years.
What the research found
The REVEAL study followed 1,730 cats across 21 countries: 1,008 with preclinical HCM and 722 apparently healthy cats.
Among the cats with preclinical disease:
- About 3 in 10 (30.5%) went on to develop congestive heart failure, a blood clot (arterial thromboembolism), or both.
- Risk built up slowly over years. Heart failure risk was about 7% at one year, 20% at five years, and 24% at ten years. Clot risk was about 3.5%, 10%, and 11% at the same points.
- Once a cat had one of these complications, average survival afterwards was a little over a year.
Those numbers sound frightening, so here is the important caveat: these cats were seen at centres able to diagnose heart disease, often because something had already been noticed. Cats whose disease is quieter may do better, and other studies in general-practice cats have reported lower rates. The study also doesn't show that any particular treatment or monitoring plan changes the outcome. It tells us the disease is real and common, not that every cat with a murmur is in danger.
The two signs that can't wait
These are the moments when a cat with heart disease, diagnosed or not, needs a veterinarian now, not tomorrow morning.
1. Fast or effortful breathing while resting or asleep
A healthy cat at rest breathes quietly, with small, easy chest movements. Watch for:
- breathing that looks fast while your cat is sleeping or lying still
- visible effort: the belly working hard, the chest heaving
- open-mouth breathing or panting (cats rarely pant unless something is wrong)
- sitting hunched with elbows out and neck stretched, reluctant to lie down
Any of these at rest means call a vet or emergency clinic now. Heart failure in cats often shows up exactly like this, sometimes after a stressful event.
2. Sudden pain, crying, or weakness in the back legs
A blood clot from the heart typically lodges where the main artery splits to the back legs. It tends to look like:
- sudden crying or yowling in pain
- dragging one or both back legs, or suddenly unable to walk on them
- back paws that feel cold, or pads that look paler or bluish compared to the front
This is an emergency. Go to a veterinarian or emergency clinic straight away.
If you're seeing either of these right now, stop reading and call.
What's worth keeping in your cat's record
Because this disease is found at the vet, not at home, the useful thing you can do is keep the history legible:
- Murmur or gallop notes: whether one has ever been mentioned, at which visit, and by which clinic.
- Heart scans: dates of any echocardiograms and what changed between them.
- Medications: what was started, when, and any dose changes.
- Breed and family history: whether your cat's breed is known to be predisposed, and anything a breeder told you.
- Resting breathing: if your vet has asked you to count breaths while your cat sleeps, log the count with the date and time, so the trend is easy to show.
And keep routine vet exams. With this disease that isn't filler advice: the exam is how it gets found.
How PAWai fits in
PAWai can't hear a heart murmur, can't screen for heart disease, and can't tell you whether your cat's heart is healthy. What it can do is keep a slow-moving heart history in one place: the first murmur noted, the scan dates, the medication changes, and any breathing counts your vet asked for. That makes the history easy to share across years and between clinics.
If your cat is struggling to breathe or has suddenly lost the use of its back legs, don't open an app. Call a veterinarian.
Read the evidence: Cats With Silent Heart Disease Faced Real Risk — the REVEAL study
Also useful: How to prepare for a vet visit
PAWai organizes information and educates pet owners. PAWai does not diagnose conditions or recommend treatment. Always consult a licensed veterinarian for medical decisions about your pet.