is called a cardiac cycle
, consisting of three stages:
1) The two atria
are in systole
(contraction), while the two ventricle
s are in diastole
(relaxation), resulting in blood
moving from the atria to the ventricles. This lasts for 0.15 seconds.
2) The two ventricles are now in systole, while the atria relax, resulting in blood moving to the lungs
, and into the body
. This lasts for 0.30 seconds.
3) Finally, both the atria and the ventricles are in diastole, a complete rest
. This lasts for 0.40 seconds.
So, the total time for one cardiac cycle is 0.85 seconds. It's these three stages which make up the sound
of the heartbeat: lub dub pause.
Control and coordination of the cardiac cycle is the job of nodal tissue