Cardiac cycle

• Diastole


  Relaxation of cardiac muscle
• Diastole


  1. As atria + ventricles relax, they expand drawing blood into atria

  2. Pressure in atria increases opening AV valves

  3. Blood passively enters ventricles

  4. SL valves close to prevent blood from leaving the heart
• Systole


  1. Atrial systole: Atria contract, forcing remaining blood into ventricles

  2. Ventricular systole: Ventricles contract forcing blood from ventricles into aorta + pulmonary artery due to pressure build up closing AV valves (prevent backflow into atria) and SL valves forced open to let blood through
• How Conduction system controls the cardiac cycle


  1. Sino atrial node initiates an electrical impulse and sends it through the atrial walls to the atrio ventricular node, causing atrial systole

  2. The impulse travels down the bundles of his, to the purkinje fibres causing ventricular systole

  3. No impulse causes diastole, where the cardiac muscle in atria and ventricles relax allowing blood to enter