The difficult thing about heart disease is that it is quiet. In cats and dogs the heart can labour for months, sometimes years, and the first thing an owner notices is often not the disease itself but its late consequence.

This page is about what to watch for at home. How the examination is done is on a separate page: echocardiography.

What you might see at home

Faster breathing at rest. The earliest and most reliable sign; how to count it is below
Difficulty breathing, using the belly, standing with the neck extended and elbows held out
Tiring quickly. Shorter walks in a dog, a cat that stops jumping
Coughing in dogs, particularly worse at night and after lying down
Fainting or episodes resembling fainting, often during excitement or effort
Lethargy, hiding, no interest in play
Loss of appetite and weight
A swollen belly from fluid collecting
Pale or bluish gums
Sudden weakness in a cat’s hind legs, with pain and cold limbs

That last one needs saying separately. In cats a clot formed inside the heart can break loose and block the artery to the hind legs. The cat suddenly cannot use its legs, cries in pain, and the legs go cold. This is an emergency measured in hours.

One point matters: none of these signs belongs to the heart alone. Lung disease, anaemia, pain and hormonal problems produce the same picture. Telling them apart takes examination and imaging.

The most useful measurement at home

This is the most valuable thing an owner can do, and it is almost never used.

With the animal in deep sleep, count one breath as the chest rising and falling once. Count for thirty seconds and double it. Do not count straight after play, in the heat, or while the animal is unsettled.

Under 30 breaths a minute at rest is normal. Consistently above 30 in sleep needs checking; above 40 needs checking the same day.

The value is not in one number but in the trend. Count on a few evenings a week and write it down; within a few weeks you know your own animal’s normal, which is more useful than any general threshold. In an animal already diagnosed with heart disease, fluid collecting in the lungs often shows first in this number, while the animal still looks well.

The method is described in detail in my cat is breathing fast.

In cats

Heart disease in cats is insidious. Cats already move little and slow down on their own when they struggle, so the stage where we would say “tiring easily” simply is not seen.

The commonest is hypertrophic cardiomyopathy: thickening of the heart muscle. A thickened heart fills less well, pressure backs up, and eventually fluid collects in the lungs. In some cats it gives no sign for years.

In cats the first sign is usually one of three things: faster breathing, sudden hind limb paralysis, or sudden death with no warning at all. That is why assessing a cat before signs appear is worthwhile, particularly where there is breed predisposition or an audible murmur.

In dogs

In dogs the picture changes with age and breed.

In older small breeds the commonest problem is the mitral valve degenerating over time. The valve no longer closes fully, blood leaks back, the heart enlarges, and the enlarged heart presses on the windpipe. That produces the classic finding: a dry cough that worsens at night and after lying down. Owners describe it as something stuck in the throat.

In large and certain specific breeds, dilated cardiomyopathy occurs: the heart muscle thins and loses contractile strength. Here the first sign is less often a cough and more often tiring quickly, lethargy and fainting.

The other causes of coughing in dogs, and what the sound tells you, are in coughing in dogs.

What a murmur does and does not mean

A murmur is not a disease, it is a sound: it says the flow of blood through the heart has become turbulent.

Not every animal with a murmur has heart disease. Young animals have innocent murmurs that disappear with growth, and anaemia and fever produce murmurs too.

Not every animal with heart disease has a murmur. This is particularly true in cats; a cat with advanced cardiomyopathy may have no murmur at all.

So a murmur is a question, not an answer. The answer comes from imaging.

The heart is not assessed alone

Heart disease rarely arrives alone.

In cats, kidney disease, high blood pressure and hyperthyroidism directly affect how the heart works, and the cardiac picture will not improve while those go untreated. The reverse is true as well: in an animal with heart disease the changes in circulation affect the kidneys, and some cardiac medications alter kidney values.

So a cardiac assessment is read, where needed, alongside blood pressure measurement, blood and urine tests, radiography and abdominal ultrasound.

Diagnosis and follow-up

Diagnosis comes from echocardiography: the chambers, the thickness of the muscle, the valves and the flow of blood inside the heart, assessed by ultrasound.

What follows the diagnosis matters as much as the diagnosis. Heart disease may progress, hold steady, or respond to treatment, and the only way to see which is to repeat the same measurements. The stage of the disease sets the interval between checks.

Between those checks, the sleeping breathing rate you keep at home is the only indicator you have.

When it is an emergency

Do not wait for:

Laboured breathing, or a cat breathing with its mouth open
Pale, grey or bluish gums
Fainting or collapse
Sudden weakness and coldness in a cat’s hind legs
A sleeping breathing rate above 40

We are open every hour. If you cannot tell whether to come now or wait until morning, nights and weekends helps; every emergency sign is on the emergency page.

Frequently asked

Can heart disease be cured

Most heart disease cannot be reversed, but it can be managed. The aim of treatment is not to remove the disease but to reduce the load on the heart, delay fluid collecting in the lungs, and lengthen the time the animal feels well. In animals caught early that time can be long.

A murmur was heard in my cat but there are no complaints

This is common and it can go either way: an innocent murmur, or a cardiomyopathy that has not yet declared itself. Listening cannot tell them apart. Assessment is advised even in a young, healthy-seeming cat, particularly if a procedure needing anaesthesia is planned.

Should an animal with heart disease exercise

Stopping exercise entirely is neither necessary nor right. Short, regular movement at the animal’s own pace is usually appropriate; hard running and exercise in the heat are not. The limit follows the stage of the disease and we tell you where it sits.

Should I switch to a low-salt food

Do not change food on your own. Diet in heart disease is planned by stage, and a restriction made at the wrong time can reduce appetite and do harm. In an animal with heart disease, continuing to eat comes before the salt content.

Is heart medication lifelong

Usually yes, and the dose is not fixed: it is adjusted on the measurements taken at each check. Do not stop the medication yourself; stopping heart failure drugs abruptly can bring the picture back quickly.