Cardiac Cycle

Cardiac Cycle

Cardiac Cycle

SYSTOLE: atria and ventricles contract
DIASTOLE: atria and ventricles relax
Both gradual processes that culminate in relaxation and contraction.

5 PHASES OF CARDIAC CYCLE:

1. ISOVOLUMETRIC VENTRICULAR RELAXATION
   AV and semilunar valves closed
   Atrial and ventricular diastole
   Atria fill
   Ventricular volume static

2. VENTRICULAR FILLING
   AV valves open, semilunar valves closed
   Atrial and ventricular diastole
   Ventricles fill

3. ATRIAL SYSTOLE
   AV valves open, semilunar valves closed
   Atrial systole, ventricular diastole
   Ventricles fill
   End diastolic volume: volume of blood in ventricles at end of phase

4. ISOVOLUMETRIC VENTRICULAR CONTRACTION
   AV valves and semilunar valves closed
   Atrial diastole, ventricular systole
   Ventricular volume static

5. VENTRICULAR EJECTION
   AV valves closed, semilunar valves open
   Ventricles empty
   End systolic volume: volume of blood in ventricles at end of phase
   End of this phase: ventricles relax, semilunar valves close

Cycle begins again.