Pet Factsheets

Heart murmurs

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A heart murmur is an abnormal sound that a vet hears when listening to the heart through a stethoscope. It can be an indication of heart disease, so other diagnostic tests may be warranted. In young kittens, innocent murmurs are essentially harmless and usually disappear by 4 months of age. To diagnose the cause of a murmur, your vet may recommend tests such as blood tests, chest radiographs (x-rays), and echocardiograms.

What is a heart murmur?

When listening to a cat's heart through a stethoscope, a vet normally hears two sounds, a "lub" and a "dub", which are the sounds of the heart valves closing as blood circulates through the heart. An additional "whooshing" sound, known as a heart murmur, is usually associated with a disturbance of the smooth blood flow through the heart.

Vets rank the intensity or loudness of a heart murmur in grades from one to six, with one being barely audible and six being the loudest. There is also a one-to-five ranking system that works the same way. These grades do not necessarily correlate with the severity of the heart condition; they are merely one of several ways that vets use to characterise the murmur.

A heart murmur is not always a cause for concern, but it may be an indication of a heart problem. Depending on your cat's condition, the vet may want to perform additional diagnostic tests to determine the cause of the murmur.

What causes a heart murmur?

Heart murmurs are caused by any number of conditions that can create turbulence in the flow of blood through the heart. In cats, common causes for heart murmurs include:

  • Hyperthyroidism (an excess of thyroid hormone)
  • High blood pressure
  • Hypertrophic cardiomyopathy (thickening of the heart muscle walls)
  • Heart valve deficiencies or blockages
  • Defects in the heart walls
  • Blood clots within the heart
  • Heartworm disease (rare)
  • Anaemia
  • Severe dehydration

What is an innocent murmur?

Occasionally, vets may detect a heart murmur in a young kitten.While this may indicate the presence of a congenital heart condition (a defect that the kitten was born with), in many cases it is an innocent murmur, meaning that it is not related to a heart problem. These murmurs usually disappear by the time the animal is about 4 months of age. If a murmur does not resolve, your vet may recommend diagnostic testing to investigate it further.

What are other signs of a heart condition?

Not all cats with a heart condition show outward signs. However, if you have been told that your cat has a heart murmur, you should watch for signs such as:

  • Difficult or rapid breathing
  • Congestion or "noisy" breathing
  • Loss of appetite
  • Unexplained weight loss
  • Weakness or lethargy (tiredness)
  • Collapse

If your cat shows signs of open-mouth breathing or panting, grey or blue gums or tongue, or leg paralysis, seek veterinary help immediately!

Which diagnostic tests will my vet recommend?

To determine the cause of a heart murmur, your vet may recommend a number of tests, such as:

  • Blood tests, including thyroid and heartworm tests
  • Chest radiographs (x-rays) to assess the heart, blood vessels, and lungs
  • An electrocardiogram (ECG)
  • An echocardiogram (an ultrasound exam to evaluate heart structure and function)
  • Blood pressure tests

How are heart murmurs treated?

Treatment depends on the cause of the heart murmur and your cat's condition. If your cat is not showing any signs of heart disease other than the murmur, your vet may choose to monitor your cat and provide treatment only if signs occur.

In some cases, such as when heart murmurs are caused by hyperthyroidism or dehydration, treatment of those conditions may resolve the heart murmur completely. However, if the murmur is caused by a congenital condition, your vet may recommend surgery. In other cases, the heart murmur may remain, but medications can help make your cat more comfortable and improve your pet's longevity.