Cardiac Cycle

• Systole

  • Cardiac Cycle: Continuous events which make up heartbeat
  • Atrial Systole:
  • When atria have filled with blood (vena cava and pulmonary vein)
  • Atrial wall muscles contract
  • Little pressure as walls are thin
  • Push blood through AV valve into ventricles
  • Semi-lunar valves in artery prevent backflow
  • Ventricular Systole:
  • Ventricles contract (~0.1s after atrial systole)
  • Thicker muscular walls of ventricles squeeze blood
  • Pushing it out (into aorta and pulmonary artery)
  • For ~0.3s
  • Atrial muscles relaxed so atria start to refill with blood
• Diastole

  • Cardiac Diastole:
  • Ventricular and atrial muscles relax
  • Ventricular pressure decrease
  • Blood from veins flows into atria
  • Distending thin walls
  • Causing pressure increase
  • Opening AV valves
  • Some blood flows into ventricles
  • Atrial muscles contract again forcing blood into ventricles (next cycle)