Can you the fact that human heart will rest twice as it works. We all know that our human heart is four chambered heart in which two auricles and two ventricles are presents. In human heart every cycle is of 0.8 sec thats why there are 72 heart beats per minutes.
When auricle is contracted for 0.1 sec then the ventricles are relaxed similarily in that manner when ventricles will contract for 0.3 sec then the auricles will relaxed. And the both auricle and ventricle were relaxed for 0.4 sec after there each contraction.
If any if my steemit friend have any doubt about this then comment i will surely replied him.