cardiac cycle Flashcards
What is the cardiac cycle?
all events that occur from the beginning of one heart beat to the beginning of the next
What are the phases of the cardiac cycle?
- Passive Filling
- Atrial Contraction
- Isovolumetric ventricular Contraction
- Ventricular Ejection
- Isovolumetric ventricular Relaxation
What occurs in passive filling?
The pressure in the atria and ventricles is close to 0 so the AV valves open allowing venous flow into the ventricles
As aortic pressure ~ 80 mmHg, the aortic valve is closed
The pulmonary valve on the right of the heart is also closed
Ventricles become ~ 80% full by passive filling
What occurs in atrial contraction?
the contraction of the atria displaces the blood into the ventricles and completes the end diastolic volume
What occurs in isovolumetric ventricular contraction?
ventricular pressure rises once it is greater than atrial pressure the AV valve closes - first heart sound ‘lub’
aortic valve is closed so blood doesnt leave
tension increases around the volume and ventricular pressure steeply rises
What occurs in ventricular ejection?
ventricular pressure > aortic/ pulmonary arterial pressure - the semilunar valves open (silent event)
SV is then ejected leaving behind the End Systolic Volume
aortic pressure rises
the ventricle then re-polarises and the ventricles begin to relax and ventricular pressure falls
once ventricular pressure < aortic/ pulmonary pressure semilunar valves shut - 2nd heart sound
SV =
EDV - ESV
What occurs in isovolumetric ventricular relaxation?
begins once the semi-lunar valves close
the pressure falls around the closed volume -isovolumetric relaxation
once ventricular pressure < atrial pressure the AV valves open (silent) & heart begins a new cycle
When is the S1 ‘lub’ sound heard?
At the beginning of systole
When is the S2 heart sound ‘dub’ heard?
At the beginning of diastole
