The heart beats 72 times per minute, i.e., that many cardiac cycles are performed per minute. From this it could be deduced that the duration of a cardiac cycle is o .8 seconds.
During a cardiac cycle, each ventricle pumps out approximately 70 ml of blood, which is called as the stroke volume. The stroke volume multiplied by the heart rate (number of beats per min) gives the cardiac output. Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and averages 5000 ml or 5 litres in a healthy individual.

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