It has its own electrical system. Explanation: The heart’s electrical system controls the timing of the heartbeat by regulating heart rate and heart rhythm. The electrical signal starts at the top of the heart, called the sinoatrial (SA) node, and travels through the heart. The atrioventricular (AV) node controls heart rate by acting as a relay station, slowing the electrical current sent by the SA node before it passes through the ventricles. The heart has four chambers and four valves.