cardiac cycle

• Cardiac cycle


  All of the physiological events associated with a single heartbeat, including electrical events, mechanical events (pressures and volumes), and heart sounds
• Cardiac cycle


  1. Atria and ventricles alternately contract

  2. Pressures in the chambers change greatly
• Systole

  The contraction phase
• Diastole


  The relaxation phase
• Atrial systole


  1. Lasts about 0.1 seconds

  2. Both atria contract and force the blood from the atria into the ventricles
• Ventricular systole


  1. Lasts about 0.3 seconds

  2. Both ventricles contract

  3. Blood is forced to the lungs via the pulmonary trunk, and the rest of the body via the aorta
• Atrial diastole


  1. Lasting about 0.7 seconds

  2. Relaxation of the atria

  3. Atria fill with blood from the large veins (the vena cava)
• Ventricular diastole


  1. Lasts about 0.5 seconds

  2. Begins before atrial systole

  3. Allows the ventricles to fill passively with blood from the atria
• Cardiac cycle


  1. At the beginning, all four chambers are in diastole

  2. Tricuspid and bicuspid valves open, blood flows into left and right auricles

  3. SA Node generates action potential, atria undergo systole pushing blood into ventricles

  4. Action potential conducted to ventricles, ventricles contract pushing blood to pulmonary artery and aorta

  5. When ventricles contract, auricles undergo diastole

  6. Increased ventricular pressure closes tricuspid and bicuspid valves

  7. Ventricular pressure opens semilunar valves directing blood flow