Cardiac Cycle

• What are the three stages of the cardiac cycle?

  • diastole
  • atrial systole
  • ventricular systole.
• What happens during diastole?

  • Atria and ventricular muscles are relaxed
  • so blood enters atria via vena cava and pulmonary vein
  • increasing pressure in atria
• What happens during atrial systole?

  • Atria muscular walls contract, increasing pressure further.
  • causes atrioventricular valves to open and blood to flow into ventricles
  • ventricular muscular walls are relaxed
• What happens during ventricular systole?

  • After a short delay (so ventricles fill), ventricular muscular walls contract, increasing pressure
  • atrioventricular valves close and semi-lunar valves open
  • blood pushed out of ventricles into the arteries
• What causes the atrioventricular valves to open?

  Higher pressure in the atria than in the ventricles
• What causes the semi-lunar valves to open?

  Higher pressure in the ventricles than in the arteries