The Cardiac Cycle

1

• The Cardiac Cycle
• Occurs in 2 parts
• Diastole ventricular relaxation
• Systole ventricular contraction

2

• The Cardiac Cycle
• Is a series of
• pressure changes,
• valve actions
• electrical potentials
• that bring about the movement of blood through
  the heart
• during one complete heart beat.
• The heart consists of two pumps
• Left pump Systemic circulation
• Right pump Pulmonary circulation

3

• The events on both sides of heart are similar.
• Difference is the pressure generated by 2
  ventricles.
• Left ventricular pressure 120mm Hg
• Right ventricular pressure 25mm Hg
• Why is this the case and what information does
  this
• provide as to the size of each half?

4

• Atrial Pressure
• Pressure within atrium increases as blood enters
  from pulmonary vein (LS)
• AV valve shut
• At end of atrial filling ventricle starts to
  relax (pressure falls)
• When atrial pressure exceeds ventricular
  pressure, AV valve pushed open
• 70-80 of blood flows from atrium into ventricle
• When atrium contracts remaining blood forced into
  ventricle.
• Ventricular pressure exceeds atrial pressure.
• Causes AV valve to close

5

• Ventricular Pressure
• AV valve closed
• Ventricle now full of blood
• Once ventricular pressure rises above pressure in
  aorta the aortic semilunar valve opens through
  which blood flows into receiving vessel.