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