Horses have a closed circulatory system. The circulatory system delivers oxygen to the body cells. The gases move from high concentration to low concentration. Oxygen from the air passes through the walls of the lungs into the blood. The blood is then pumped around the body by the heart. At the same time, carbon dioxide goes from the blood into the lungs and is exhaled.
The heart is actually two pumps. It has two ventricles which suppy two circulatory systems. In one system, blood is circulated through the lungs, where it picks up oxygen and releases carbon dioxide. In the second system, blood with oxygen is circulated around the body releasing oxygen and collecting carbon dioxide.
