Heart Murmurs in Horses

By Deidre M. Carson, BVSc, MRCVS & Sidney W. Ricketts, LVO, BSc, BVSc, DESM, DipECEIM, FRCPath, FRCVS.

A heart murmur is an abnormal sound that originates from the heart valves and can be heard with a stethoscope skillfully placed over the heart valves.

Are all murmurs the same?

heart_murmurs-1Most murmurs are functional, i.e., they are not due to any significant abnormality but are caused by normal 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, thickening or narrowing of a valve or large blood vessel 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 cycle (systole or diastole).  They can be heard on both or best on one or the other side of the chest and over specific valves.

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. These include reduced exercise tolerance, filling (thickening) of the limbs and lower neck or chest (edema) and enlargement of blood vessels, particularly causing an obviously visible pulse in the jugular vein ('jugular pulse').

Skillful auscultation (listening with a stethoscope), combined with the presence or absence of clinical signs of heart disease, will enable your veterinarian to localize the murmur to a specific area or valve of the heart and 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, either to try to predict whether it represents a performance-limiting problem or to find out if it will get worse.

A blood test may help to tell if there is damage to the heart muscle. An electrocardiogram may be performed to look at the electrical conductivity of the heart for abnormalities in heart size and heart rhythm.

The most useful examination that can be performed is an ultrasound scan (echocardiographic) examination. This allows the heart 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. These abnormalities can be detected with an echocardiogram.

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?

heart_murmurs-2Many fit and healthy horses have heart murmurs. Most horses are unaffected in their performance but in some cases, there may be a progression of the abnormality causing the murmur and the horse's performance may deteriorate with time. The above tests should answer the following questions:

1. Is the horse safe to ride at the desired level?

2. Will the murmur affect the horse in the future, either in terms of value or performance?

Occasionally, a murmur may be a temporary complication following a viral infection that 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.

Murmurs cannot be treated medically or surgically in the horse. 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.

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