The Cardiac Cycle

• What are the three stages of the cardiac cycle?

  1. Diastole
  2. Atrial Systole
  3. Ventricular Systole
• Describe the events of diastole.

  • Atria and ventricular muscular walls relaxed.
  • Blood enters the atria via the vena cava and the pulmonary vein.
  • Blood flowing into the atria increases the pressure.
  • Atrioventricular valves are closed.
• Describe the events of atrial systole.

  • Atria muscular walls contract, reducing the volume of the chambers, causing a further increase in pressure.
  • This causes atrioventricular valves to open and blood to flow into the ventricles.
  • The ventricular muscular walls are still relaxed.
• Describe the events of ventricular systole.

  • After a short delay, ventricular muscular walls contract, increasing the pressure beyond the atrial pressure.
  • This causes the atrioventricular valves to close and the semi-lunar valves to open.
  • Blood is pushed out of the ventricles into the pulmonary artery and aorta.
• How do you calculate cardiac output?

  Cardiac output= heart rate x stroke volume
• What is cardiac output?

  The volume of blood pumped out of one ventricle per minute.
• What is heart rate?

  Beats per minute.
• What is stroke volume?

  The volume of blood pumped out per heartbeat.
• What is the role of valves?

  They ensure blood flow is unidirectional by preventing backflow.
• What are the two types of valves found in the heart?

  1. Atrioventricular valves
  2. Semi-lunar valves
• When do atrioventricular valves open?

  When pressure is higher in the atria than in the ventricles.
• When do semi-lunar valves open?

  When the ventricles are at a higher pressure than the aorta and pulmonary artery.