Female Speaker: The heart is a pump, which drives blood circulation through the body. In fact, it is two pumps. The right side we see is oxygen-poor blood from the body, seen here in blue, and pumps it to the lungs. The left side we see is the freshly oxygenated blood from the lungs, seen here in red, and pumps it to the rest of the body. The cardiac cycle or the heart's pumping sequence begins with a period of relaxation when the blood fills the heart. Then the heart contracts and pushes blood through the semilunar valves and into the aorta and arteries, which are the body's pipelines. The entire cycle takes less than a second.