cardiac cycle phases

1) Quiescent period.

• none of chambers contracting 
• blood flows in to atria directly in to ventricles through open atrioventricular valves.

2) Atrial systole.

• Atria depolarise [P wave] and contract.
• additional blood forced into ventricles
• at end of phase, end diastolic volume = 130ml blood 
• 70% of end diastolic volume enters passively during quiescent phase
• last 30% added by atrial systole

3) Isovolumetric contraction

• Atria relax, remain is diastole for rest of the cycle
• ventricles depolarise [QRS] and contract
• ventricular pressure ries rapidly 
• atrioventricular valves close 
• contraction…