Describe the different steps involved in the pumping action of the heart

Cardiac cycle refers to the sequence of events which occur from the beginning of

one heart beat to the beginning of the next heart beat.

- In the cardiac cycle, the phase of contraction of any heart chamber is called

systole and the phase of relaxation of any heart chamber is called diastole.

- A complete heart beat consists of one systole and one diastole of each of the atria and of the ventricles.

- The action potential generated by SA-node stimulates both the atria to undergo a

simultaneous contraction – the atrial systole. This increases the flow of blood into the ventricles by about 30 per cent.

- The action potential is conducted to the ventricular side by the AVN and AV

bundle from where the bundle of HIS transmits it through the entire ventricular musculature. This causes the ventricular muscles to contract,

ventricular systole, the atria undergoes relaxation (diastole).

- As the ventricular pressure is increased the semilunar valves guarding the

pulmonary artery (right side) and the aorta (left side) are forced open, allowing the blood in the ventricles to flow through these vessels into the circulatory pathway.

- As the ventricular muscle relax, the ventricular diastole starts.

- There is a decrease in the ventricular pressure which cause the closure of

semilunar valves which prevents the backflow of blood into the ventricles.

- Then the AV valves open and blood starts flowing into the ventricles, even before the atrial systole starts.