Busselton Vet Hospital Library

Heart Disease

yellow paws

Learn About Heart Disease in Pets

Heart disease is a term that encompasses very broad range of diseases that affect the heart’s ability to do its job properly. Heart disease is significantly more common in dogs than in cats, and affects about 10% of our canine friends. Heart disease includes murmurs (abnormal sounds due to blood flowing abnormally), and arrhythmias (abnormal heart rhythm due to problems with electricity flow).

Types of Heart Disease

Heart conditions are either classed as congenital, meaning present from birth, or acquired, meaning they developed over your pet’s lifetime. Acquired diseases are far more common, accounting for about 95% of cases.

The most common types of heart disease we encounter are mitral valve disease (MVD) and dilated cardiomyopathy (DCM) in dogs, with the former being significantly more common. In cats, we tend to encounter hypertrophic cardiomyopathy (HCM), and a blood clotting condition called Feline Aortic Thromboembolism (FATE). As mentioned before, cardiac issues in cats are far less common, but we still keep an eye out for them.

Signs of Heart Disease that You Might See

The signs of heart disease that you may notice at home are very variable and vague, as similar symptoms can occur with other disease processes, and not all symptoms are present with all forms of heart disease. Symptoms in cats are also quite rare as they are very good at hiding them. Symptoms can include:

  • Reluctant to exercise, or tiring more quickly
  • Lethargy/depression
  • Weakness
  • Breathing more quickly or more heavily at rest or when sleeping
  • Restlessness, particularly at night
  • Appetite and drinking changes
  • Fainting, more commonly with exercise
  • Weight loss

Pets with heart failure may have more severe signs such as extreme difficulty breathing or respiratory distress, changed gum colour, abdominal swelling, collapse/fainting, and more, and should be presented to your vet as an emergency

Diagnosing Heart Disease

As your vet, we might suspect heart disease based on some things you mention when you bring your pet in for a consultation. We also listen carefully to your pet’s heart, listening to rate, rhythm, and for any murmurs. Some changes to the heart sounds may be fairly mild, and we may not do anything further at the time other than recommend annual monitoring, which is easily done by coming in for your pet’s annual vaccinations.

If we are concerned, we may recommend further tests to assess the severity of disease so that we can better understand your pet’s condition and the best way to manage it. This may include an ECG (looking at the electrical impulses of the heart), chest x-rays, and possibly even a heart ultrasound (echocardiography). On rare occasions, we may need to refer you to a specialist.

Four Stages of Heart Disease – A, B (1 and 2), C, and D

These stages are for grading Mitral Valve Disease in dogs, as it is by far the most common heart condition we encounter, but it can provide a rough guideline for other heart conditions.

A – High risk of heart disease (at-risk breed), but no symptoms or abnormal clinical exam findings

B – A murmur or other early sign of heart disease is present, but no symptoms of heart disease

B1 – the heart shape is still normal on x-rays and ultrasound

B2 – the heart shape is changed

C – there are signs of heart failure, or have previously has signs of heart failure but is responding to medication

D – there are signs of heart failure, and it is not responding to standard treatment

So My Dog Has Heart Disease – Now What?

Most forms of heart disease are not curable, only manageable. Some forms, usually the congenital ones, can be treated and resolved surgically, but regular monitoring is still advised.

Medical management depends on stage and severity. Stages A and B1 don’t require treatment, but it is recommended that Stage B1 patients go through screening every year to monitor for progression. Dogs in Stage B2 are advised to start early treatment options as this can improve their expected lifespan by a significant margin, by keeping them at this stage for as long as possible.

Stages C and D require multiple medications, and in some cases intensive in-hospital management is needed to try get a patient through a severe failure episode and stabilised. Not all pets will progress to these stages, but it is something that needs to be remembered.

What About Cats?

Picking up heart disease early in cats is much harder, as the signs are often very subtle and not that different from normal cat behaviour, and they rarely have changes to their heart sounds that we can hear. Cats with heart disease are most often diagnosed when they present with symptoms that indicate heart failure, such as severe difficulty breathing or respiratory distress, collapse, or in the case of FATE, paralysis in the back legs. We usually start with getting them stabilised and comfortable, and if we determine heart failure was the cause, we can start on an appropriate management plan.


Mitral Valve Disease
MVD is the most common heart condition we encounter. This is when the valve between the top and bottom chambers of the left side of the heart thickens and does not seal properly, which allows some blood to flow in the wrong direction when the heart beats. We hear this as a whooshing sound when we’re listening to your dog’s heart.

It is more common in small dogs, with Cavalier King Charles Spaniels, Poodles, Jack Russell Terriers and Chihuahuas being some of the more likely breeds to be affected.

Dilated Cardiomyopathy
DCM is when the chambers of the heart stretch, and the heart muscle becomes too weak to pump blood effectively. This one is a bit trickier for vets to find, as it doesn’t always cause changes to the heart sounds we hear. It is often diagnosed when your pet presents with symptoms that can point to a possible problem with the heart, or is discovered when investigating another issue.

This is more common in large dogs, with Dobermans and Boxers being a significant number of these cases, but can also affect German Shepherds, Great Danes, Springer Spaniels, and St Bernards, among others.

Hypertrophic Cardiomyopathy
A condition of cats, this is when the heart muscle thickens, leaving very little room for blood to flow through, and doesn’t work well as a pump. Cats are very often only diagnosed when they present with symptoms of heart failure.

Feline Aortic Thromboembolism
A complication that most commonly occurs as a result of heart disease, but can sometimes occur for other reasons. This is when a large clot forms in part of the biggest artery in the body, and becomes stuck, blocking the blood supply to the back legs. This is an emergency condition, and unfortunately often has a poor outcome.

If you have any other questions or problems, please feel free to phone the hospital for advice at (08) 9752-1433.

We provide a 24-hour emergency service. Phone (08) 9752-1433 anytime and follow the prompts.