Cardiac cycle

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Cardiac cycle

Definition

The change occur in heart during one heart beat, this process continue repeated in sequence manor called cardiac cycle.

Duration of cycle


  • Heart rate - 70 - 80 / min.
  • Average - 75 /  min.
  • One heart beat - 60/75 = 0.8 sec.


Each cardiac cycle is starts from spontaneous generation of impulses by SA node, this impulse travel from SA node to AV node through intermodal fibers than bundle of his than right and left bundle branch than purkinge fibers than it distributes all myocardium.

Heart, cardiac cycle, events
Events of cardiac cycle


Events of cardiac cycle

Atrial events ( 0.8 sec )

1. Atrial systole  ( 0.1 sec ).
2. Atrial diastole ( 0.7 sec ).

Ventricular events ( 0.8 sec )

1. Ventricular systole ( 0.3 sec ).
2. Ventricular diastole ( 0.5 sec ).

Ventricular systole ( 0.3 sec )

1. Isovolumetric phase ( 0.05 sec ).
2. Rapid ejection phase ( 0.1 sec ).
3. Reduce ejection phase ( 0.15 sec ).

1. Iso-volumetric phase ( 0.05 sec )


  • Valve - close all valves.
  • Heart sound - 1st heart sound produce.
  • Ejection - not start.
  • Contraction - begins.
  • Volume - same ( not change ).

2. Rapid ejection phase ( 0.1 sec )


  • Valve - semilunar valve are open and atrio-ventricular (AV) valve are remain closed.
  • Heart sound - no.
  • Ejection - rapidly.
  • Contraction - continue.
  • Volume - reduced fastly.

 3. Reduced ejection phase ( 0.15 sec )


  • Valve - semilunar valve are open and AV valve remain closed.
  • Heart sound - no.
  • Ejection - slowly-slowly.
  • Contraction - continue.
  • Volume - reduced.

Ventricular diastole ( 0.5 sec )

1. Proto-diastolic phase ( 0.04 sec ).
2. Iso-volumetric relaxation ( 0.06 sec ).
3. Rapid filling phase ( 0.1 sec ).
4. Slow filling phase ( 0.2 sec ).
5. Last rapid filling phase ( 0.1 sec ).

1. Proto-diastolic phase ( 0.04 sec )


  • Valve - closer of semilunar valve and AV valve are already closed.
  • Heart sound - 2nd heart sound produce.
  • Filling - not starts.
  • Relaxation - ready to beginning.
  • Volume - remain end diastolic volume ( 60ml ).

2. Iso-volumetric relaxation ( 0.06 sec )


  • Valve - all valves are closed.
  • Heart sound - no.
  • Filling - not start.
  • Relaxation - ventricle relaxed.
  • volume - no change.

3. Rapid filling phase ( 0.1 sec )


  • Valve - open AV valves.
  • Heart sound - 3rd heart sound produce.
  • Filling - rapidly
  • Relaxation - already relaxed.
  • Volume - increase ( 70% filling ).

4. Slow filling phase ( 0.2 sec )


  • Valve - AV valve remain open and semilunar valve are closed.
  • Heart sound - no.
  • Filling - slowly-slowly.
  • Relaxation - already relaxed.
  • Volume - ( 20% filling only in this phase ).

5. Last rapid filling phase ( 0.1 sec )


  • Valve - AV already open and semilunar remain closed.
  • Heart sound - 4th heart sound produce.
  • Filling - rapidly.
  • Relaxation - already relaxed .
  • Volume - both chamber complete filled ( 10% filling only in this phase ).
Location:India India

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