Understanding cardiac cycles

Hyderabad: Soon, the SAN generates a new action potential and the events described in our earlier article are repeated in that sequence and the process continues.

This sequential event in the heart, which is cyclically repeated, is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles.
As mentioned earlier, 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 0.8 seconds.

During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood which is called the stroke volume.

The stroke volume multiplied by the heart rate (no. 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.

The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output. For example, the cardiac output of an athlete will be much higher than that of an ordinary man.

During each cardiac cycle two prominent sounds are produced, which can be easily heard through a stethoscope.
The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance.

To be continued…