Heart Murmurs in Horses: A Quick Guide For What Owners Should Know

Heart Murmurs in Horses: A Quick Guide For What Owners Should Know

Your horse’s heart is extraordinary, working tirelessly to power movement, health and performance. But when a vet mentions a heart murmur, it can feel worrying, confusing, and full of unanswered questions. That’s why our recent IH Masterclass with Professor Gunther van Loon, one of the world’s leading equine cardiologists from Ghent University, was such a gift.

Professor van Loon very rarely teaches directly to horse owners — usually his work is shared within veterinary and academic circles — so having his time, knowledge and kindness in explaining complex subjects was genuinely special. He guided us through what murmurs and irregular rhythms really mean, how they are properly assessed in clinical practice, and how vets weigh up performance, welfare and safety.

It was packed with clarity, reassurance, and solid science… and if you haven’t watched the recording yet, you absolutely should.

In the meantime, here’s a quick, accessible guide to help you make sense of the key points from the webinar — what murmurs are, what they don’t automatically mean, and how to approach them calmly and sensibly for your horse’s sake.

But truly… do watch the full recording when you can. This was a special one.

1. What is a murmur, in plain English?

• A heart murmur is simply an extra or unusual sound that a vet hears when listening to the heart with a stethoscope.
  • A normal heartbeat is a clear “lub–dub, lub–dub” (two main sounds per beat).
  • A murmur is a whoosh / hiss / musical noise heard around those two sounds, caused by turbulent blood flow inside the heart or the big vessels leaving it.
• Common causes of that turbulence include:
  • A slightly leaky valve (blood going backwards when it shouldn’t)
  • A narrowed area or small hole the blood is being forced through
  • Less commonly, changes in the blood itself (e.g. very thin/anaemic blood)
• Key points for you as an owner:
  • A murmur is a description of a sound, not a diagnosis.
  • Some murmurs are harmless “incidental” findings and horses still work and compete normally.
  • Others indicate a more serious problem and need ultrasound (echo) and sometimes ECG to know:

2. Murmurs that are often low concern

(Provided a vet has checked properly)

• Soft, quiet murmurs (especially in young or fit horses) where:
  • The horse has normal performance
  • Heart size on ultrasound is normal
  • No arrhythmias (abnormal rhythms) on ECG, including during exercise
• Certain small congenital defects (like small ventricular septal defects) can be:
  • Well compensated
  • Compatible with normal work or even competition, if echo/ECG parameters are good and monitored.

Note: If the heart is structurally normal, the chambers aren’t enlarged, and rhythm is good – many murmurs are more of a “note and monitor” than a crisis.

3. Murmurs that deserve closer attention

These don’t automatically mean disaster, but they must be properly assessed:

• Mitral regurgitation (often a systolic murmur on the left):
  • If mild and chambers are normal → often rideable with checks.
  • If leakage is moderate–severe and the left atrium enlarges, risk of atrial fibrillation goes up.
• Aortic regurgitation (often in older horses, diastolic/long murmur):
  • Can silently enlarge the left ventricle.
  • Enlarged ventricle + certain arrhythmias (on exercise ECG) = increased risk of collapse/sudden death.
  • Loud, “musical” murmur doesn’t always mean worse disease – ultrasound + ECG are what matter.
• Any murmur plus:
  • Reduced performance unexplained by lameness or lungs
  • Nosebleeds during/after exercise (especially in non‑racehorses)
  • Collapse or near-collapse
  • Ventral edema or abnormal jugular vein pulsation

…should trigger prompt cardiac investigation.

4. What good assessment looks like

When a murmur is found, the sensible next steps are often:

1. Clinical exam + detailed auscultation (where, when in the cycle, how it sounds).
2. Echocardiography (ECG)
   • Valve function
   • Chamber size (any dilatation?)
   • Pump function
   • Test during rest and during controlled exercise if there’s concern (especially for aortic regurgitation or performance issues).

From these, a cardiology‑savvy vet can usually say:

• “Safe to ride; recheck every X months/years,” or
• “Ride with limits and monitor closely,” or
• “Not safe to ride (risk too high).”

5. Your practical take‑home

• A murmur is not an automatic death sentence or retirement order.
• Never base decisions on loudness alone.
• For peace of mind and safety, ask your vet about an ECG, and put together a plan for re‑assessment?”