Heart Murmurs Horses

A heart murmur is an unusual sound heard during the heartbeat when listening with a stethoscope. Instead of the normal "lub-dub" sound of a healthy heart, a murmur adds an extra sound or changes the quality of the normal sounds. Discovering that your horse has a murmur can be alarming—the word "murmur" sounds serious and suggests something's wrong with the heart. But here's what you need to understand: not all murmurs are pathological, not all murmurs matter, and many horses with heart murmurs live completely normal lives and never have issues from them. Some murmurs are absolutely concerning and warrant investigation and management. Others are benign and require only periodic monitoring. The challenge is understanding which category your horse's murmur falls into.

What's important to know is that a murmur is a symptom, not a diagnosis. Hearing a murmur tells your vet something is happening with the heart—either blood is flowing abnormally because of a valve problem, or the heart itself has structural issues. But a murmur doesn't immediately tell you whether that something is serious, whether it will affect your horse's health, or whether treatment is needed. Understanding the specific cause of the murmur, which requires further investigation beyond just listening, determines what the murmur actually means for your horse.

Murmurs are classified by several characteristics: location (which part of the heart produces the sound), timing (when during the heartbeat the murmur occurs), duration (how long the murmur lasts), intensity (how loud it is), and character (what it sounds like). These characteristics help your vet determine the likely cause and whether further investigation is warranted. A soft, quiet murmur heard only at certain times might be benign. A loud, prominent murmur present continuously might suggest significant heart disease.

The reality is that discovering a murmur at a routine exam when your horse is clinically normal is common and often not urgent. Many horses have murmurs that never cause problems. Some murmurs are discovered as incidental findings that require monitoring but no treatment. Some murmurs indicate disease that will eventually become problematic and warrant management. A small percentage of murmurs indicate serious disease requiring investigation and possibly restricting the horse's activity. Understanding what your horse's specific murmur means requires investigation and discussion with your vet, not panic.

This guide explains what heart murmurs are, what causes them, how they're classified, what investigation is appropriate, what different types of murmurs mean for your horse, and how to manage a horse with a murmur. You'll understand why some murmurs are concerning and others are basically ignored, what further investigation might be needed, and what having a murmur means for your horse's future.

Heart murmurs develop when blood flow through the heart becomes turbulent or unusual. The normal heart has smooth blood flow that produces normal, quiet sounds. When something changes the flow pattern—a valve doesn't close completely and blood leaks backward, a valve opening is narrowed and blood flows forcefully through it, or structural changes alter blood flow—turbulence develops. Turbulent flow creates sound, which is the murmur. Understanding that a murmur is just sound produced by altered blood flow helps you understand it's a sign of altered flow, not necessarily disease.

Valve disease is one of the most common causes. Heart valves are one-way gates ensuring blood flows in the correct direction. If a valve doesn't close completely, blood leaks backward, creating turbulence and a murmur. This is called regurgitation or insufficiency. If a valve opening is narrowed, blood flows forcefully through the narrow opening, creating turbulence and a murmur. This is called stenosis. Some valve disease is minor and never impacts function. Some is significant and compromises cardiac efficiency.

Age is a risk factor for some murmurs. Older horses develop valve problems more frequently as valves wear with age. Young horses sometimes have innocent murmurs that change or resolve as they grow. The murmur heard in a young horse might disappear by adulthood, or might persist without causing problems. Older horses developing new murmurs warrant investigation because age-related valve disease is significant.

Congenital heart disease (present at birth) causes some murmurs. Some horses are born with valve defects or structural abnormalities. Some of these horses never show symptoms and live normal lives. Others have significant disease affecting function and lifespan. Detecting congenital heart disease early allows appropriate management.

Infection can damage the heart and cause murmurs. Bacterial infections seeding the heart, endocarditis, or myocarditis create inflammation that damages cardiac structures and produces murmurs. Strangles is a classic example—septic infection that can seed the heart and cause valve damage with resulting murmurs. Some infection-related cardiac damage resolves, some is permanent.

Trauma to the chest can damage the heart and cause murmurs. A horse that falls or is struck in the chest might develop cardiac damage. Most recover uneventfully, but some develop permanent damage resulting in murmurs.

Athletic horses sometimes develop murmurs. The exact relationship between performance and murmur development isn't fully understood, but some athletic horses develop murmurs that don't necessarily affect their ability to perform. This is why a screening echocardiogram might be recommended for performance horses to establish a baseline.

Other conditions including anemia, fever, or severe systemic illness sometimes cause functional murmurs—murmurs that develop secondarily to other problems rather than from primary heart disease. These murmurs often resolve once the underlying condition is treated.

A murmur itself is the sign—an abnormal sound heard through the stethoscope. Your vet detects it during physical examination. Most horse owners never know their horse has a murmur unless their vet mentions it, because you can't hear a murmur without a stethoscope. A horse with a benign murmur is often completely asymptomatic—no clinical signs whatsoever. The murmur is discovered on routine exam and might cause initial concern but represents nothing serious.

Early warning signs that a murmur might be significant include exercise intolerance—the horse tires more easily than expected. A murmur causing significant cardiac compromise might manifest as reduced athletic ability, reluctance to work, or fatigue during activities previously tolerated. Some horses develop cough, sometimes associated with fluid developing in the lungs from cardiac insufficiency. Others show difficulty breathing or respiratory distress, particularly with exercise.

Physical findings that suggest a murmur is significant include irregular heart rhythm heard on auscultation alongside the murmur, elevated resting heart rate, weak pulses, or signs of fluid accumulation like leg swelling or distended jugular veins. A horse with just a murmur and no other cardiac findings is usually reassuring. One with a murmur plus other cardiac abnormalities is more concerning.

Behavioral changes sometimes accompany significant murmurs. A horse feeling generally unwell from cardiac compromise might seem less enthusiastic, more withdrawn, or show attitude changes. These are nonspecific signs that could indicate many problems, but in the presence of a murmur, they warrant investigation.

The absence of symptoms despite a murmur is common and often reassuring. Many horses with murmurs are completely healthy clinically. The murmur is an incidental finding that never causes problems. This is worth remembering when worried about a newly discovered murmur—symptoms would likely have developed if the murmur was significant, particularly in a horse you interact with regularly and would notice changes in.

Progression of symptoms matters more than their presence. A horse that's had a murmur for years with stable exercise tolerance and no symptoms is likely dealing with benign or nonprogressive disease. One that develops worsening exercise intolerance or new symptoms suggests disease progression warranting investigation and management.

Emergency signs accompanying a murmur warrant immediate attention. Collapse, syncope, severe respiratory distress, or acute inability to move require emergency evaluation regardless of a known murmur.

When your vet discovers a murmur, the initial conversation involves characterizing the murmur. Your vet describes its characteristics: location, timing, duration, intensity, and character. These characteristics help suggest what might be causing the murmur. Your vet also assesses how significant it sounds and whether other cardiac findings are present.

The decision about whether further investigation is needed depends on murmur characteristics and your horse's clinical signs. A soft, quiet murmur in a young horse with no clinical signs might warrant no further investigation—young horses sometimes have innocent murmurs that don't indicate disease. A loud murmur with other cardiac findings or clinical signs of cardiac compromise warrants further investigation. Your vet helps you make the decision about whether further diagnostics are appropriate.

Echocardiography is the primary diagnostic tool for investigating a murmur. Your vet uses ultrasound to visualize the heart structures and assess what's causing the murmur. This test reveals whether a valve is truly defective, whether chambers are enlarged, whether the heart muscle is thick or damaged, and numerous other details about cardiac structure and function. Often echocardiography reveals exactly what's causing the murmur and allows assessment of how significant it is.

Electrocardiography (ECG) records the heart's electrical activity and might reveal arrhythmias or electrical abnormalities. This test is sometimes done alongside echocardiography but often isn't necessary when the physical findings suggest a structural problem.

Blood work might be done to assess overall health and rule out conditions like anemia that could cause functional murmurs. Specific cardiac biomarkers might show whether the heart muscle is damaged.

Interpretation of findings determines next steps. Investigation might reveal that the murmur is caused by minor valve leakage that requires no treatment and no activity restriction. The horse is monitored periodically but managed normally. Alternatively, investigation might reveal significant cardiac disease requiring activity restriction, medication, or close monitoring. Knowing what the murmur is caused by and how significant it is determines appropriate management.

Treatment depends on the diagnosis. Some murmurs from valvular disease benefit from medication supporting cardiac function. Others don't require specific treatment but need monitoring. Some murmurs indicate conditions that need activity restriction to prevent complications. Others don't require any management at all beyond periodic monitoring to ensure disease isn't progressing.

Managing a horse with a benign murmur requires essentially nothing—live your life normally with the horse. Many horses have murmurs never causing problems, never affecting their ability to perform, never requiring any management or medication. Discovering a benign murmur is reassuring once you understand it doesn't warrant concern.

Periodic monitoring is reasonable for most horses with murmurs. Annual or biennial recheck exams let your vet reassess the murmur and ensure it hasn't changed. Most benign murmurs remain stable. One that significantly changes or develops associated findings might warrant further investigation. This periodic monitoring is simple—just including cardiac assessment in your regular vet exams.

For horses where a murmur is found to be significant, management becomes more involved. Activity restrictions might be recommended. A horse with significant valve disease might need light work rather than intense performance. Some horses can continue normal activity with cardiac medication. Others need stall rest or pasture living only. The specific restrictions depend on the cardiac diagnosis and severity.

Medication management, if needed, requires consistency. Horses on cardiac medication need regular administration and periodic rechecks to ensure medication is working and no dose adjustments are needed. Maintaining the medication regimen is essential for horses whose murmurs are managed medically.

Monitoring for changes is important. A horse with a known murmur should have any changes in exercise tolerance, development of respiratory symptoms, or other changes reported to your vet. Detecting disease progression early allows management adjustments.

For competition horses or horses requiring clearance for sale, addressing a murmur early through appropriate investigation prevents issues later. A murmur discovered before purchase can be investigated and documented, allowing informed decisions. A murmur discovered after purchase might create complications or liability issues. Transparent disclosure and investigation of murmurs protects both buyers and sellers.

Decision-making about activity and workload for a horse with significant murmur should balance what the horse's heart can tolerate with what maintains the horse's mental wellbeing. A horse too restricted might suffer psychological distress. One worked too hard might damage the heart. Finding the appropriate balance keeps the horse healthy and happy within the limits his cardiac condition allows.

Prevention of cardiac disease that causes murmurs starts with practices supporting overall cardiac health. Vaccination against infectious diseases that can seed the heart reduces risk of infection-related valve damage. Prompt treatment of systemic infections prevents them from affecting the heart. Good management, appropriate conditioning, and minimizing stress support cardiac health. Proper nutrition including adequate minerals supports cardiac function.

Early detection through regular exams helps identify murmurs when they first develop. A murmur discovered at routine exam when the horse is asymptomatic allows investigation and management before clinical problems develop. Regular auscultation as part of veterinary exams is important.

Prognosis for horses with benign murmurs is excellent—most never cause problems and never affect the horse's lifespan or quality of life. Many horses with benign murmurs are never even told they have murmurs because the finding is so clinically irrelevant.

Prognosis for horses with significant valve disease depends on the severity. Many can live for years with appropriate management and activity restriction. Some have progressive disease requiring increasing management over time. Most remain functional and have acceptable quality of life despite the murmur and cardiac disease.

Long-term outlook depends on whether a murmur is detected early, whether appropriate investigation reveals its significance, and whether management is implemented appropriately. A horse with a benign murmur has essentially normal outlook. One with significant murmur managed appropriately often lives many years with good quality of life. One with serious disease that goes unmanaged might have complications or reduced lifespan.

The key to managing a horse with a murmur is understanding what it means. Whether it's incidental and benign, or significant and requiring management, knowing what you're dealing with allows appropriate decision-making. Many horses carry heart murmurs throughout their lives without ever showing problems, living completely normal functional lives. That reassuring reality is worth remembering when first learning your horse has a murmur.