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The horse’s heart is one very large muscle; it has four chambers and supplies blood to all parts of their body from birth until death.

rachaelBy Dr Rachael Glebocki MRCVSBy Dr Rachael Glebocki MRCVS

The four chambers of the heart include: right atrium where deoxygenated blood is returned from the body, the right ventricle pumps blood into lungs to refill with oxygen via pulmonary artery: the left atrium which receives oxygenated blood: and the left ventricle which sends that rejuvenated blood out into the body via the aorta. The size of this muscle system is roughly 1% of the overall body weight and weighs around 3-4kg and pumps 26 to 37 litres a minute. The heart is made of a specialised muscle cell, the cardiac muscle which is designed for pumping. There are also pacemaker cells located in the right atrium that regulate rhythm through electrical impulses. The four chambers of the heart include: right atrium where deoxygenated blood is returned from the body, the right ventricle pumps blood into lungs to refill with oxygen via pulmonary artery: the left atrium which receives oxygenated blood: and the left ventricle which sends that rejuvenated blood out into the body via the aorta. The size of this muscle system is roughly 1% of the overall body weight and weighs around 3-4kg and pumps 26 to 37 litres a minute. The heart is made of a specialised muscle cell, the cardiac muscle which is designed for pumping. There are also pacemaker cells located in the right atrium that regulate rhythm through electrical impulses. 

Depending on how fit your horse is will relate to the heart rate and its recovery time (time taken for the heart rate to go back to its normal level after intense exercise). You can check your horse’s heart rate via a digital pulse just above the fetlock or feeling under the jaw, a very light touch is required. A normal resting heart rate for the average adult horse is between 28-40 beats per minute. 

Horses with heart disorders or defects may have a general loss of condition, become fatigued easily (particularly after exercise), have difficulty breathing or shortness of breath, and show signs of weakness (including fainting or collapse). In addition, excess fluid that has accumulated in the lungs, limbs, jugular vein, under the chest or abdomen may indicate heart failure. Horses can cough because of this fluid accumulation. Signs may show up only after exercise, but over time they may occur even when the horse is at rest.

What to expect from a typical veterinary examination on my horses heart?

Imaging techniques include x‑rays (which are not commonly performed in horses due to their size), electrocardiography (recording electrical activity of the heart), and echocardiography (a type of ultrasonography).The physical examination they perform will involve using a stethoscope to listen to the heart and the lungs. A veterinarian may hear an abnormal heart rate (for example, a rate that is too slow, fast, or irregular), an abnormal breathing rate (fast or laboured breathing), a murmur (an abnormal sound caused by abnormal blood flow or vibrations in the heart), decreased or muffled heart sounds, or abnormal sounds in the lungs that suggest fluid accumulation. A veterinarian will also feel the horse's pulse (which may feel rapid, weak, or irregular) and examine the horse's gums for evidence of blue, purple, or grey colour, a sign that oxygen is not reaching the body's tissues adequately. The veterinarian will also examine the limbs and abdomen for signs of fluid accumulation.

Heart murmurs are graded on a scale of 1 to 6, 1 being the least severe, to 6 being the most severe. Low grade murmurs will normally not affect your horses performance but should be monitored on a regular basis to establish whether they are progressing or not. 

If you are at all concerned about your horse’s heart please contact your vet.

Veterinary advice in this magazine is provided as a general guide Veterinary advice in this magazine is provided as a general guide and you should always seek professional advice.

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