Outline how a heartbeat is initiated and controlled

The heart is myogenic, meaning it initiates its own muscle contraction. At the Sinoatrial Node (SAN), found in the right atrium, an electrical impulse is generated that spreads across the atria, causing them to contract. The impulse then reaches the Atrioventricular Node (AVN) which delays the signal, allowing the atria to fully contract. Non-conductive tissue at the bottom of the atria prevents the ventricles from contracting too early, allowing them to fill with blood. The wave of excitation is then sent down the Bundle of His and along Purkyne tissue to the base of the heart, causing the ventricles to contract from the bottom up and forcing the blood out into the arteries at the top.