A. Closing of AV valve
B. Opening of A.V. valve
C. Opening of semilunar valve
D. Beginning of Q wave.
This phase is Isovolumic relaxation phase .
B i.e. Opening of A.V. value.
Cardiac events during isovolumetric relaxation:
- Once the ventricular muscle is fully contracted, the already falling ventricular pressures drop more rapidly.
- The aortic and pulmonary valves close at this stage.
- After the valves are closed, pressure continues to drop rapidly during the period of isovolumetric ventricular relaxation.
End-stage of Isovolumetric relaxation:
- This phase ends when the ventricular pressure falls below the atrial pressure and the AV valves open, permitting the ventricles to fill.
- The filling is rapid at first, then slows as the next cardiac contraction approaches.
- Atrial pressure continues to rise after the end of ventricular systole until the AV valves open, then drops and slowly rises again until the next atrial systole.