Heart murmurs

Heart murmurs are quite common in horses and are often detected during a routine veterinary examination or at pre-purchase examination.

A heart murmur is an abnormal sound heard when the horses heart is listened to with a stethoscope.

Murmurs are heard when there is abnormal flow of blood through the heart. If the flow of blood moving through the heart is disrupted in any way an unusual sound will be heard either between or after the heart beats. The flow of blood in the heart can be disrupted when it goes through the valves which separate the upper and lower chambers of the heart (the atria and ventricles) or if the consistency of the blood changes.

Some murmurs are benign or functional, which means they are not causing any problems to the horses heart or circulation and should not affect your horses performance.
Other murmurs are pathological, which means they may affect your horses health and performance either in the immediate or more distant future. These murmurs are usually caused by a problem with one of the valves in the heart or due to a birth defect affecting the heart.
Horses suffering with colic often have murmurs when the vet listens to their heart, this is usually due to the horse being dehydrated resulting in the blood being thicker than normal and so the flow through the heart is affected.
Murmurs can range from very quiet to very loud. Your vet will grade the murmur on a scale of 1 (faint murmur) to 6 (very loud). Murmurs can be heard on the left side of the heart, the right side or both sides. Your vet may be able to tell that a murmur is associated with a particular valve within the heart for example: the mitral valve on the left which divides the left atrium from the left ventricle or the tricuspid valve on the right which divides the right atrium from the right ventricle.

Most murmurs are detected on routine examination by your vet, for example when they listen to your horses heart before giving it sedation or vaccinating it. Sometimes murmurs start to affect the health of the horse and so your vet will detect them when they have been called to examine the horse for another reason such as poor performance, lethargy or weight loss, which are the most common signs of heart disease.

If your vet detects a heart murmur not only will they listen very carefully to the heart to grade the murmur and try to determine its significance but they will also examine the rest of your horse for any signs that the murmur may be causing a problem. Sometimes it is straight forward for your vet to tell if the murmur is benign or pathological because of the sound of the murmur. Some murmurs however can be more difficult to determine if it is benign or pathological.
If your vet detects a pathological murmur they may also be able to tell what is causing the murmur and how it is likely to affect your horse. However, sometimes it can be very difficult to determine the exact cause of the murmur or if it is causing any problems to the heart. If your vet is not certain of the nature or consequences of the murmur, they may advise that your horse needs further tests such as echocardiography.

Your vet may advise that your horse needs to have an ultrasound examination of their heart, this is also called echocardiography.
Echocardiography requires a very advanced ultrasound machine and so your vet may refer your horse to a specialist for this procedure. Echocardiography allows us to see the horses heart in real time. Using echocardiography we can determine the cause of the murmur, eg a disease of one of the valves or a birth defect. If the heart is compromised by abnormal blood flow it may get bigger and so ultrasound allows us to measure the different heart chambers to check that they are coping with the abnormal flow. These measurements helps the vet decide if the murmur is likely to affect your horses performance or health.
Other tests may include an electrocardiogram which can detect abnormalities in the heart rhythm which are sometimes found if the heart is not coping very well with the abnormal blood flow.