Heart murmurs are frequently detected in apparently healthy horses during a routine physical examination or a pre-purchase examination and may indicate presence of heart disease. However, physiologic “functional” murmurs not associated with any heart disease are also commonly found in horses. Differentiation of physiologic (functional) from pathologic heart murmurs can be difficult or impossible based on physical examination and auscultation alone.
Valvular insufficiency is the most common heart disease associated with a heart murmur in horses. Congenital heart disease can cause murmurs in horses but is less common while valvular stenosis is very rare in horses.
Heart murmurs are characterized based on their timing, intensity ("loudness"), location and quality.
Systolic (between S1 and S2)
Early, mid or late systolic
Pansystolic – from the start of S1 to the end of S2
Holosystolic – from the end of S1 to the start of S2
Diastolic (between S2 and S1)
Early, mid or late diastolic
Holodiastolic - from the end of S2 to the start of S1
Grade 1: Very soft localized murmur that requires extended auscultation in a quiet environment to detect.
Grade 2: Readily audible quiet murmur that is localized and softer than the normal heart beats (S1 and S2)
Grade 3: Readily audible murmur that is moderately loud and similar in volume to S1 and S2.
Grade 4: Readily audible murmur that radiates widely and is louder than S1 or S2.
Grade 5: Very loud murmur with a palpable thrill (vibration) over the heart.
Grade 6: Very loud murmur associated with a palpable thrill that is audible with the stethoscope held just off the chest.
PMI (Point of maximal intensity):
Mitral valve area: left, 5th intercostal space, ~10cm below the point of the shoulder
Aortic valve area: left, 4th intercostal space, dorsally to the mitral valve area
Pulmonic valve area: left, 3rd intercostal space, slightly ventral
Tricuspid valve area: right, 4th intercostal space, midway between the point of the shoulder and olecranon. This
Crescendo (becoming louder from the start)
Descescendo (becoming quieter from the start)
Not all heart murmurs cause substantial problems for the horse. However, some do. The best way to determine whether your horse could have a clinically relevant heart murmur is through an echocardiographic examination.