How does the heart initiate and control its own heartbeat?

So the heart originates its own heartbeat by itself - this is called myogenic muscle - and doesnt need any nerve impulse to stimulate it, so is different to all the other organs in the body. The sino-atrial node (SAN) above the atria originates this impulse and sends it downwards to the atrio-ventricular node (AVN). This downwards moving signal allows the atria to contract downwards i.e. atrial systole. Then the AVN's function is to collect the signal and pass it to the Purkyne fibres/Bundle of His (differently named according to A level exam board being studied). Its other function is to delay the signal slightly to allow the atria to finish contracting before the ventricles do, as this would confuse blood flow. The function of the Purkyne fibres/Bundle of His is to transport the impulse to the apex of the heart (i.e. the bottom corners) and convey it upwards. This upwards moving signal allows the ventricles to contract upwards i.e. ventricular systole. This is useful so that the ventricles force blood up into the pulmonary artery and aorta and out of the heart. Underlined - the 3 key players in originating and controlling heart beat Bold - key phrases identified in mark schemes