Pressure changes and valves

• Atrial systole

  • SL valve closed and AV valve open due to end of previous cycle
  • atrium contracts — forces blood into ventricles so pressure in atrium increases
  • pressure in aorta falls as blood flows away from heart
• ventricular systole

  • ventricle contracts - increasing ventricular pressure
  • ventricular pressure exceeds atrial pressure - closing AV valve
  • more contraction increases pressure
  • Ventricular pressure exceeds aortic pressure - forcing SL valve open
  • blood enters aorta and volume of blood in ventricle decreases
  • pressure in aorta increases
  • pressure in ventricle decreases
• diastole

  • ventricular pressure continues to fall due to relaxation - when brown aortic pressure closes SL valve
  • atrium filling again and pressure rises - when exceeds ventricular pressure - forces AV valve open
  • pressure in aorta falls
  • pressure higher in atrium - keeping AV valve open