Prodiastolic and isomertric relaxation period::
The aorta and pulmonary trunk recoil and blood tries to rush back into the respective ventricles but this is suddenly stopped by the swift closure of semilunar valves this produces the second heart sound heralding the end of ventricular systole The interval between the start of ventricular diastole and the closure of SL valves (0.04 sec) is known as prodiastolic period the next to this period is isometric relaxation period (0.08 sec) This is the period during which both the valves (AV and SL) are closed but ventricles and atria are in diastolic condition Thus this is the period when intra-ventricular pressure is minimum and heart is relaxing
Rapid and slow inflow period::
The isometric relaxation period ends with the opening of AV valve and because ventricles are under diastolic condition rapid inflow of blood starts This is known as rapid inflow period Third heart sound is heard on echophone at this juncture and it lasts for 0.03 sec the next phase is slow inflow period (0.2 sec) and is also known as Diastasis
As seen in when ventricular diastole is about to end the atrial systole has started and it overlaps for 0.1 sec During this phase because of active contraction of atria filling of ventricles start rapidly This is called rapid filling period and fourth heart sound is heard at this stage on echophone
ECG Changes::
The events of cardiac cycle,s can be traced on ECG During atrial systole P wave is seen QRS seen in the beginning of ventricular systole The last T wave can be seen in the beginning of ventricular diastole
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