Cardiac cycle

Last revised by Joachim Feger on 17 Dec 2021

The cardiac cycle describes the electrical and mechanical actions of the heart, contraction and relaxation of the atria and ventricles during every heartbeat.

The cardiac cycle consists of the following phases 1-3:

  • isovolumetric contraction and closure of the atrioventricular valves 
    • electrical trigger: QRS complex
    • intraventricular pressure buildup
  • opening of the semilunar valves and rapid ejection
    • maximal outflow
    • build-up of systolic artery pressure
  • decreased ejection 
    • electrical trigger: ventricular repolarization (T wave)
    • decline in ventricular tension
    • continuous rise in atrial pressure
  • isovolumetric relaxation and closure of the semilunar valves 
    • fall in intraventricular pressure
    • eventually leading to an atrioventricular pressure gradient
  • opening of the atrioventricular valve and rapid filling
    • early inflow due to the lower ventricular pressure
    • rapid fall in atrial pressure
  • slow filling 
    • equalization of intraarterial and intraventricular filling pressures (diastasis)
  • atrial contraction
    • electrical trigger: P wave
    • late ventricular filling (about 10-15% at rest and up to 40% at high heart rates)

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