Since the SA node is at the top of the atrial mass, the atria contract from th

The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. Atrial systole is the contraction of the heart muscle (myocardia) of the left and right atria.


As you know the SA is a pacemaker which helps in setting the rhythm of contraction so that the blood can flow to the ventricle and just like that there is a Atrio-ventrical node in the ventricles ,which is situated in the septum, which helps in pushing the blood to the lungs and the whole body.

Hope this helps