Heartbeat:

The relaxation of heart chambers fills them with blood and the contraction of chambers propels the blood out of them. The alternating relaxations and contractions make up the cardiac cycle and one complete cardiac cycle makes one heartbeat.

Steps involved in the complete cardiac cycle:

The complete cardiac cycle consists of the following steps.

Cardiac diastole:

The atria and ventricles relax and blood is filled in the aria This …. is called cardiac diastole

Atrial systole:

….

Ventricular Systole:

Now both ventricles contract and pump the blood towards …. and lungs. The period of ventricular contraction is called …. Systole.

The duration of one heartbeat:

In one heartbeat, diastole lasts about 0.4 sec, atrial systole …. about 0.1 sec, and ventricular systole lasts about 0.3 sec.

Lubb-dubb:

When ventricles contract the tricuspid and bicuspid valves …. "lubb" sound is produced. Similarly, when ventricles relax, the semilunar …. closes, and a "dubb” sound is produced. "Lubb-dubb" can be heard with the help of a stethoscope.