Heart and circulation
Introduction
The heart is the most important muscle in the body as it must pump blood rich in oxygen and nutrients to the entire body.
The right side of the heart receives blood from the body that is depleted of oxygen and is full of carbon dioxide (waste product) and pumps it to the lungs. The lungs take this deoxygenated blood, and remove carbon dioxide, while adding oxygen from inspired air. The left side of the heart receives the oxygen-rich blood, and pumps it to every part of the body. There are 4 valves within the heart, atrioventricular and semilunar valves, which keep blood flowing in one direction to prevent mixing of oxygenated and deoxygenated blood. Deoxygenated blood flows from the body to the right atrium. It then goes through the tricuspid valve and into right ventricle where it is pumped through the pulmonic valve and into the lungs.
Once the blood circulates through the lungs it becomes oxygenated and returns to the heart. Here it goes into the left atrium, through the mitral valve, into the left ventricle, and then out through the aortic valve and to the rest of the body.
Horses are usually presented for relatively minor clinical signs in comparison with many small animals. It is relatively uncommon for horses to be presented with overt cardiac failure and the vet, therefore, must establish whether currently asymptomatic disease may deteriorate and become a problem in the future or whether clinical signs of heart disease, such as exercise intolerance, are a cause of heart disease or if the problem results from abnormalities in other body systems.
Unlike diseases of many other organ systems, cardiovascular diseases generally do not resolve but almost always become more limiting and may lead to death. In addition, cardiovascular diseases may be more difficult to diagnose because the heart cannot be seen and is protected so well by the rib cage. Therefore, evaluation of the heart depends on heart sounds, the electrocardiogram, radiology and echocardiology.