is equivalent to one complete heartbeat- during which both atria and ventricles contract and then relax.
brief rise in aortic pressure caused by backflow of blood rebounding off of semilunar valves
normal length of the cardiac cycle
average bpm is 75 and so the length of the cardiac cycle is 0.8 second. of this time atrial contraction takes 0.1 second, followed by atria relaxation and ventricular contraction, which is 0.3 second. lastly, it takes 0.4 second for the ventricles to relax. when the heart rate increases, the last variable is the one that will shorten.
lub the first heart sound and is associated with the closure of the AV valves at the beginning of the ventricular systole