Describe the events in the cardiac cycle.

1. Atrial Systole (0.7 sec): In this event atria contracts due to the wave of contraction initiated by the SA node. The blood flow takes place in ventricles as the two valves are open.

2. Ventricle Systole (0.5 sec): After this, contraction of ventricles starts taking place due to the wave of contraction initiated by the AV node. Thus closing of the two valves occur and first heart sound is produced ‘club’.

3. Complete Ventricular Systole: After ventricular contraction, the blood flows into the pulmonary trunk and aorta as the semilunar valves are opened.

4. Ventricular Diastole: In this event, the ventricles relax and the semilunar valves close and the second heart sound is made ‘dub’

5. Complete Ventricular Diastole: The opening of bicuspid and tricuspid valves take place as the pressure of ventricles lowers down and blood flows from atria to the ventricles. 0.8seconds will take for the cycle to occur.

In double circulation, deoxygenated and oxygenated blood remains separated and do not mix.