Cardiac cycle

Cardiac Cycle

Cardiac cycle is the complete sequence of events in one heartbeat. Three main stages : Diastole ,  Atrial systole and ventricular systole. 

1. Late diastole ( Relax ):  - Both atria and ventricles relax .

                                              - Atrioventricular (AV) valve open .

                                              - Semilunar valves close. 

                                              - Now , ventricles are filling with blood . ( 75-85% volume of chambers )

2. Atrial systole ( contraction ) : - The contraction exerts pressure on the blood within the atrial chambers which forces open the                                                                            bicuspid & tricuspid valves ( AV valves ) .

                                                         - Blood flows into the ventricles through the open AV valves .

                                                         - Ventricles expand .

                                                         - Ventricles now contains an average volume of about 130 ml of blood at the end of ventricular                                                                            diastole .(end- diastolic volume )