A heart murmur may be heard by your veterinary surgeon when he listens to your cat's heart. A heart murmur is caused by turbulent blood flow within the heart or the large vessels exiting the heart. This results in an abnormal noise which can be detected by the vet during examination. Heart murmurs are assessed and graded according to certain criteria. Grades I-VI are documented (I being the most mild and VI the most severe) and recorded. The grading system is based largely on how loud the murmur is compared to the other normal heart sounds but other factors are also considered.

The grade of the heart murmur does not necessarily correlate with the degree of severity of the heart problem. Some severe heart conditions in cats are not associated with a heart murmur (see cardiomyopathy information sheet).

Although many heart conditions are associated with heart murmurs there are also various other conditions that can cause a heart murmur. In young kittens, heart murmurs may be heard at first examination as an incidental finding but these may well not be present at examination 6 months later. Anaemia is another cause of heart murmurs in cats but the cats often show other signs of lethargy and anorexia as well. Cats may also have incidental murmurs as adults and this is called a “physiological murmur” - ie. the blood flow within the large vessels exiting the heart can be heard as a murmur simply put, but this is usually of no clinical significance and does not result in clinical disease.

When a heart murmur is first detected in a cat, any other clinical signs that would alert the vet to other clinical problems (ie. lethargy, abnormal respiratory pattern/rate/effort, pale gums) are assessed and investigations will be performed to establish the underlying problem. If however the cat is very well at home, shows no other clinical signs of a problem and exercises normally, then your vet may suggest a repeat examination in 3-6 months time to reassess the heart murmur and see if it has changed in anyway or if the cat has developed any other clinical signs. Often if the cat is well and the heart murmur is unchanged, periodic examination will be recommended. The only way to determine if there is any disease within the heart itself that may be causing the murmur is to perform a detailed ultrasound examination (normally performed in the conscious animal) of the heart (this is a specialist procedure and will often require a highly experienced specialist) together with an ECG if indicated.