Heart & Circulation

In valvular heart disease, one or more heart valves no longer close fully, so blood flows back (insufficiency) and a heart murmur becomes audible. The most common form is degenerative thickening of the mitral or aortic valve, often an incidental finding on auscultation; many horses remain able to work for years, while advanced cases can limit performance.

Atrial fibrillation is an arrhythmia in which the heart's atria are excited in a disordered and very fast way, making the heartbeat irregular. It is considered the most common performance-limiting arrhythmia of the horse and often only becomes noticeable through declining performance, as the large equine heart can compensate for it at rest for a long time.

In aortic rupture, the wall of the great body artery (aorta) or a vascular structure near the heart tears, leading to massive internal bleeding. It occurs mainly in older breeding stallions and often in connection with exertion or covering, and frequently ends as sudden death — an acute emergency with no reliable means of rescue.

In thrombophlebitis, a vein wall becomes inflamed and a blood clot (thrombus) forms in the vessel, in horses most often in the jugular vein. It often arises after venous catheters, injections or irritant medications and is usually clearly visible; with occlusion or infection of the vessel, complications threaten.

In myocarditis, the heart muscle itself becomes inflamed, often following viral or bacterial infections or through toxic influences. The inflammation can weaken the pumping power and trigger arrhythmias; it is a serious disease that can lead to heart failure and belongs under veterinary monitoring.

In endocarditis, usually bacteria colonise the heart lining and especially the heart valves, forming inflammatory deposits there, so-called vegetations. These damage the valves, produce a heart murmur and can wash small infectious fragments into the circulation; the disease is serious and often runs with persistent or recurrent fever.