Heart murmurs in horses: when should you act?

What exactly is a heart murmur?

A heart murmur is an extra sound the vet hears through the stethoscope, on top of the normal heart tones. It is caused by turbulent blood flow through or past the heart valves. We know this phenomenon in humans too. It does not automatically mean something is wrong with the heart itself. In horses, heart murmurs are graded on a scale of 1 to 6, where grade 1 is barely audible and grade 6 can be heard even without a stethoscope. Grades 1 to 3 are usually functional and benign; grades 4 to 6 almost always call for further investigation.

Functional versus pathological murmur

The most important distinction a vet makes is between a functional and a pathological murmur. A functional murmur has no structural cause and sometimes even disappears at a higher heart rate or after exercise. A pathological murmur points to an abnormality of the heart valve or the heart wall. The most common cause of a pathological murmur in horses is valve insufficiency, where a valve does not close properly and blood flows back. The mitral valve and aortic valve are most frequently involved. Congenital heart defects do occur but are less common.

Signs that point to a serious problem

• Reduced performance without a clear alternative cause
• Becoming tired quickly during relatively light work
• Swollen legs or abdomen due to fluid retention (oedema)
• Irregular heart rate or visible restlessness after exercise
• Spontaneous weakness, stumbling, or near-falling without an identifiable reason
• Grade 4 or higher on auscultation, combined with the above complaints

Investigation: from stethoscope to ultrasound

When the vet detects a murmur, the grade and the moment in the cardiac cycle (systolic or diastolic) determine the next step. A diastolic murmur is more often considered significant than a systolic one. Follow-up investigation typically consists of echocardiography (cardiac ultrasound) and an ECG, sometimes combined with an exercise ECG. With an echo the vet can assess valve function, the size of the heart chambers, and blood flow. Give your vet as complete information as possible: how long you have noticed something, at what levels of exertion, and how frequently. Through the horse profile in EquiSight you can keep track of observations so that you immediately provide a complete picture at every consultation.

• Echocardiography: gold standard for valve assessment
• Resting ECG: detects rhythm disorders
• Exercise ECG: reveals hidden arrhythmias
• Blood test: rules out anaemia or infection as a cause

What does this mean for use and workload?

A horse with a grade 1 or 2 functional murmur and no additional symptoms can in most cases continue to be ridden and trained as normal. With a confirmed valve insufficiency, the advice depends on the severity: a mild leakage of the tricuspid valve in a leisure horse calls for annual monitoring but does not immediately force retirement. For competition horses or intensively used show jumping or dressage riders, stricter standards apply; some examining vets will reject a horse at grade 3 or higher. Discuss a realistic management plan with your vet and set reminders via the EquiSight calendar for periodic heart check-ups.

Prevention and monitoring in practice

Heart murmurs can rarely be prevented, but early detection makes a significant difference. Have the heart listened to as standard at every annual health examination. Keep track yourself of whether your horse takes longer than normal to recover after exercise, and log this in the horse profile. EquiCoach can recognise patterns based on entered health and training data and alert you to changes that justify further investigation. An early-detected valve abnormality gives you and your vet the most room to make well-considered decisions.