Outline the events that occur within the heart, which cause blood to move around the body.

One of the most crucial functions of the heart is to act as a pump which distributes the blood around the body. The blood is first collected in the atria, and then pumped from atria to the ventricles. The atrio-ventricular valves open to allow the bloodflow from atria to ventricles, while semi-lunar valves close to prevent backflow from the arteries to ventricles. The blood is then pumped out from the ventricles to the arteries. Open semi-lunar valves allow flow from ventricles to arteries, while closed atrio-ventricular valves prevent backflow to the atria. The pressure generated this way is what causes the blood to move around the body. Pacemaker initiates each heartbeat.