The cardiac cycle

• Heart beats by contraction and relaxation of cardiac muscle
• It’s co ordinated by electrical activity and accompanied by heart sounds - from the valves in heart closing
• One complete relaxation and contraction is one heartbeat
• Valves open when pressure in front of them is greater - forces valve open
• When pressure after valve exceeds pressure before it - pushing or blood towards valve closes it
• Valves on open in one direction - blood flow unidirectional
• Contraction of atria using atrial muscle called atrial systole

  contraction of ventricles using ventricular muscles called ventricular systole
• relaxation of the heart muscle called diastole
• Diastole

  • heart relaxed
  • AV valves open - atria and then ventricles fill up with blood
  • SL valves closed to prevent back flow of blood from previous beat
• Atrial systole

  • begins at right atrium - quickly spreads to left to co ordinate heartbeat
  • atria contract - squeeze blood into ventricles
  • muscles close at top of veins preventing back flow
• Ventricular systole

  • ventricles contract and squeeze blood through arteries - SL valves open and AV valves closed
• Cardiac output = stroke volume x heart rate
• During exercise

  • body needs more oxygen and glucose for increased respiration to increase release of energy for muscle contraction
  • heart rate will increase
• With time cardiac muscle become stronger and contract harder which increases the stroke volume - same cardiac output but lower heart rate