The cardiac cycleThis presentation goes through the stages of the cardiac cycle that occur in one heart beat.The cycle has been depicted here as starting from the end of diastole when the ventricles are relaxed and filled with blood.
Phase 1: Isovolumetric ContractionThe left ventricle isfull of blood andbegins to contract.This causes thepressure in the leftventricle to increase.
Phase 1: Isovolumetric ContractionOnce the pressure inthe left ventricleexceeds that of theleft atrium the mitralvalve will close.This is to preventblood from goingback into the leftatrium. Mitral valve closes
Phase 1: Isovolumetric ContractionThe ventriclescontinue tocontract, but until theaortic valve opens thepressure in the leftventricle increaseswith no change involume- this isisovolumetric Isovolumetriccontraction. contraction
Phase 2: Ventricular ejectionOnce the pressure inthe left ventricleexceeds that of theaorta the aortic valvewill open. Aortic valve opens
Phase 2: Ventricular ejectionBlood then leaves Ventricular ejectionthe left ventricle intothe systemiccirculation via theaorta- ventricularejection
Phase 3: Isovolumetric relaxationThe ventricles now Aortic valve closesbegin to relax oncethe blood has beenejected.When the pressurein the left ventriclefalls below that ofthe aorta the aorticvalve will close. Thisprevents bloodflowing back into theleft ventricle fromthe aorta.
Phase 3: Isovolumetric relaxationAs the ventriclesrelax the pressurewill fall, but therewill be no change involume until themitral valve opens-this is isovolumetric Isovolumetericrelaxation relaxation
Phase 4: Ventricular fillingOnce the pressure inthe left ventricle fallsbelow that in the leftatrium the mitralvalve will open.This then allows theventricles to fill withblood from the leftatrium, preparing Mitral valve opensthe ventricles foranother round of thecardiac cycle.
The cardiac cycle- recapPhases of the cardiac cycle: I. Isovolumetric contraction Systole II. Ventricular ejection III. Isovolumetric relaxation Diastole IV. Ventricular filling