The cardiac cycle

• What are the stages of the cardiac cycle?

  1. Cardiac diastole
  2. Atrial systole, ventricular diastole
  3. Atrial diastole, ventricular systole
• What happens during the first stage of the cardiac cycle?

  CARDIAC DIASTOLE

  1. heart is relaxed
  2. blood at a low pressure flow into the atria
  3. atrial pressure increases as they fill
  4. some blood flows passively through open AV valves into relaxed ventricles below
• What happens during the second stage of the cardiac cycle?

  ATRIAL SYSTOLE, VENTRICULAR DIASTOLE

  1. when the atria are full, they go into atrial systole
  2. atria contract -> blood is pushed through AV valves into ventricles
  3. atrial pressure increases due to contractions
  4. ventricular pressure increases as they fill with blood
• What happens during the third stage of the cardiac cycle?

  ATRIAL DIASTOLE, VENTRICULAR SYSTOLE

  1. ventricular pressure is greater than atrial pressure, so AV valves close to prevent backflow
  2. semi-lunar valves open due to high ventricular pressure
  3. blood leaves the heart
  4. ventricles relax (ventricular diastole), semi-lunar valves close
• What happens during one cardiac cycle?

  The atria and then the ventricles contract so that blood that has entered the heart is pumped out
• Periods of contraction are called systole
• Periods of relaxation are called diastole