What is a heart murmur?
A heart murmur may be heard by your vet when he or she listens to your cat's heart. A heart murmur is caused by turbulent blood flow within the heart or the large vessels exiting from the heart. This results in an abnormal noise which can be heard by your vet when listening with a stethoscope.
How are heart murmurs assessed?
Heart murmurs are assessed and graded according to certain criteria. Grades I-VI are recognised, with Grade I being the most mild, and Grade VI the most severe. The grading system is based largely on how loud the murmur is, but other factors are also considered, such as the area over which the murmur is audible.
The grade of the heart murmur does not necessarily relate to the degree severity of the underlying heart problem. Some severe heart conditions may not associated with any heart murmur at all, and some quite loud murmurs may occur with relatively small defects.
Causes of heart murmurs
Although the presence of a murmur usually implies an underlying heart condition, murmurs can sometimes have other causes.
In young kittens, so-called 'innocent' heart murmurs may be heard as an incidental finding. These are usually no longer present when the kitten is older. Anaemia is another cause of heart murmurs in cats, but the cats often show other signs of lethargy and anorexia as well. Occasionally cats are reported to have incidental murmurs as adults, and this is called a 'physiological murmur' - e.g., the blood flow within the large vessels exiting the heart may occasionally be heard as a murmur, but this is usually of no clinical significance and does not result in clinical disease.
What to do when a heart murmur is detected
When a heart murmur is first detected in a cat, any other clinical signs that would suggest an underlying problem (e.g., lethargy, abnormal breathing pattern or effort, pale gums) are assessed and investigations will be performed to establish the underlying problem. This may involve further examinations such as an X-ray of the heart or a cardiac ultrasound examination (echocardiography).
If however the cat is very well, is showing no other clinical signs of a problem, and exercises normally, then your vet may suggest a repeat examination in a few months to reassess the heart murmur and see if it has changed, 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 of the heart. This is completely painless and is normally performed in a fully conscious cat. Your vet may suggest that you take your cat to a specialist vet for this to be done. Other tests sometimes recommended may include an ECG (an electrical tracing of the heart) and perhaps some blood tests to look for any potential underlying causes of heart disease.
In addition to heart murmurs, another abnormality that may occasionally be heard is a 'gallop' sound (an extra heart sound), which usually suggests that there is significant heart disease present, and further investigations will usually be warranted.