The Cardiac Cycle & the Pathway of Blood (AQA GCSE Physical Education (PE))

The Cardiac Cycle & the Pathway of Blood

• The cardiac cycle is:

All of the events taking place within a single heartbeat

• Each cardiac cycle contains the following events:

  • Diastole

    • The heart muscle relaxes and the chambers fill with blood

  • Systole

    • The muscle walls of the heart chambers contract and blood is forced out

      • Atrial systole forces blood out of the atria and into the ventricles

      • Ventricular systole forces blood out of the ventricles and into the arteries

    • Note that during systole the left and right-hand sides of the heart contract at the same time

Cardiac cycle diagram

During diastole the heart muscle relaxes and during systole the heart muscle contracts

Pathway of blood through the heart

• Blood travels through the chambers of the heart during a single cardiac cycle as follows:

Blood pathway table

Blood pathway diagram

Blood flows through the left and right sides of the heart at the same time

The role of valves

• Valves inside the heart prevent the backflow of blood between the ventricles and the atria, and between the arteries and the ventricles

• Valves open due to pressure differences between the different areas of the heart

  • E.g. when the atria contract the pressure in the atria is higher than the pressure in the ventricles; the valves between the atria and ventricles are forced open

• Valves also close due to pressure differences:

  • E.g. when the ventricles contract the pressure in the ventricles is higher than the pressure in the atria; this forces the valves between the atria and the ventricles to close, preventing backflow