A heart murmur is an abnormal sound which originates within the heart and surrounding large blood vessels and which can be heard with a stethoscope.

Are all murmurs the same?

Most murmurs heard in horses are not due to any significant abnormality but are caused by slightly turbulent flow of blood through a normal heart and vessels. However, some murmurs do indicate an abnormality in blood flow and/or heart function. Such abnormalities include a leaking heart valve which allows backflow of blood or an abnormal hole between different heart chambers.

Murmurs can be loud or soft, long or short, or occur at different times during the heart’s pumping action (systole or diastole). They can be heard on the left or right side of the chest or sometimes on both sides.

How can I find out if a murmur is due to a significant problem?

Most murmurs are detected with a stethoscope during routine veterinary examination for insurance or purchase or at the time of a routine check up. In nearly every case, the horse or pony has not shown any clinical sign of heart disease such as reduced exercise tolerance, thickening of the limbs and chest (oedema) and enlargement of blood vessels or an obviously visible pulse in the jugular vein (‘jugular pulse’).

Careful auscultation (listening with a stethoscope), combined with the presence or absence of clinical signs of heart disease, will enable your veterinary surgeon to localise the murmur to a specific area of the heart and usually give some indication of whether or not the murmur represents a real problem.

What other tests can be done?

In some cases it is necessary to investigate a murmur further. This helps define the cause of the murmur into one of 3 categories: firstly, there is no problem and the murmur is of no consequence; secondly, the murmur represents a potential problem in the future and will require monitoring; or thirdly, the murmur represents a definite problem in the heart and the horse should not be ridden.

A blood test may help to tell if there is damage to the heart muscle. An electrocardiogram might be performed to look for abnormalities in heart rhythm.

The most useful examination which can be performed is an ultrasound scan of the heart (echocardiography). This allows the heart and its structures to be imaged while it is beating. Heart chamber size and movement can be measured and heart valves observed opening and closing. In problem cases, the valves may be abnormally thick, may not close fully or the chambers may not pump efficiently. More expensive 'heart scanners' have what is known as 'colour flow doppler ultrasound' where blood flow can be observed in various parts of the heart to establish whether the flow is normal or not.

It is often necessary for examinations to be repeated at intervals of days, weeks or months to monitor any changes in heart structure and/or function and to give an indication of whether or not the condition is likely to be progressive.

What is the outlook for my horse if he has a murmur?

Very many fit and healthy horses have heart murmurs - the mere presence of a murmur is not necessarily a bad thing. The important thing is to establish whether or not the murmur is anything to worry about.

Occasionally, a murmur may be a temporary complication following a viral infection which may cause changes to the cardiac muscles. This is not a common occurrence, but can be monitored with blood tests. These cases should be given plenty of time off for rest and recuperation.

In some instances it may be necessary to reduce the level at which the horse is expected to compete or perform, or to retire him. Some horses with significant cardiac abnormality may not be safe to ride.