Heart Murmurs in Horses

Last Updated on April 15, 2022 by Allison Price

Horses make heart murmurs

High velocity blood flow can cause heart murmurs. Although murmurs are more common in horses with heart disease, they can also be heard in horses that have normal blood flow. It is important to identify the cause of a murmur by determining its location, timing and intensity. Although the quality and radiation of murmurs can be described, they are not as useful in determining the cause.

Your veterinarian can determine reasonable differential diagnoses, sometimes even a definitive diagnosis, by understanding how heart sounds relate to anatomy, physiology, pathophysiology and underlying anatomy. To fully assess the heart rate and rhythm without missing any anomalies, it is important to carefully examine all areas of the chest that surround the heart.

Heart Murmurs in Horses

S1 and S2 are normally audible. These sounds correspond to the closure of the atrioventricular or semilunar valves. Horses may also hear the S3 or S4 heart sounds. These low-frequency heart sounds, which are amplified by the bell of a stethoscope, occur during diastole. S3 is due to rapid ventricular filling, while S4 is due to ventricular filling caused by atrial contraction.

Diagnosing Horse Heart Murmurs

A murmur’s location is the place where it is most audible (or at its maximum intensity). This can be described as either left or right, apical, or basilar. It may be possible to distinguish the pulmonic area in horses from the aortic area at the left base of the heart. Other areas of the thorax may be affected by murmurs, though they are less prominent than those at the PMI.

A murmur can be either continuous, diastolic or systolic. The length of the murmur may help determine when the murmur is occurring. Systole’s period is generally longer than systole’s. You can also palpate the carotid pulse to determine the timing of a murmur. A systolic murmur occurs with or without the pulse. A scale from 1 to 6 is used to grade the intensity and loudness of murmurs.

  1. After extended auscultation, a very soft focal murmur can be heard in quiet areas.
  2. A soft, focal murmur which is easily audible (softer than the S1 or S2)
  3. Moderately loud murmuration with radiation (similar intensity as S1 and S2)
  4. Loud murmur that radiates far (louder than S1 or S2)
  5. A loud, palpable murmur and a palpable thrill
  6. A very loud murmur and a thrilling sound can be heard when the stethoscope is positioned on the chest wall.

Horses’ Heart Murmurs

Below are brief descriptions of some possible causes for heart murmurs in horses.

  • Aortic Regurgitation A leak at the valve that connects the left ventricle to the aorta, usually caused by infection or age-related degeneration.
  • Mitrial Regurgitation A leak at the valve that connects the left ventricle to the atrium. This is usually caused by infection or age-related degeneration.
  • Tricuspid Regurgitation A leakage at the valve connecting the right ventricle to the atrium. This can be seen in normal horses, or could be due to age-related degeneration.
  • Pulmonic Regurgitation A leak at the valve that connects the right ventricle to the pulmonary artery, which can be seen in horses with normal temperaments
  • Physiologic murmur (low grade) – Normal blood flow is heard across the heart, pulmonic valve or sometimes the mitral.
  • Ventricular Septal Decline – This is the most common congenital horse heart defect.
  • PDA (normal in the first week of life). – A normal vessel that connects the aorta to the pulmonary artery. It should close soon after birth.
  • Aortic Stenosis (rare). – Congenital malformations of the aortic valve.
  • Pulmonic Stenosis (rare). – Congenital malformations of the pulmonic vale (between the right ventricle & pulmonary artery).
  • Aortocardiac fistula is an acquired defect that causes a hole between the aorta and the right ventricle.
Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!