CARDIAC CYCLE

• Isovolumetric Relaxation

  • Happens during Diastole (Atrium and Ventricles relax)
  • Ventricular Pressure = decreased
  • Ventricular Pressure = relatively greater than Atrial pressure but below the Aortic Pressure
  • Both heart valves are closed (Atrioventricular and Semilunar)
  • No Blood flow in and out of ventricle happens so no change of ventricular pressure
• Atrial Diastole / Passive Ventricular Filling:

  • Atria are relaxed.
  • Atrial pressure is low but slowly increases as the atria fill with blood.
  • When atrial pressure is greater than ventricular pressure, the atrioventricular valve opens, and blood flows passively from the atrium to the ventricle.
• Passive Filling occurs as blood flows from higher to lower pressure without atrial contraction.

  • First half: Rapid filling of the ventricle.
  • Second half: Slow filling, causing a plateau as the pressure gradient decreases.
• Atrial Systole / Active Ventricular Filling:

  • Atria contract, increasing atrial pressure.
  • The ventricles fill further, and ventricular volume increases.
  • The ventricles start to contract, and when ventricular pressure exceeds atrial pressure, the mitral valve closes, signaling the first heart sound.
  • At the end, atrial contraction (active filling) ensures the ventricles are fully filled with blood, which results from heart muscle contraction.
• Isovolumetric Contraction

  • Ventricular pressure is greater than Atrial pressure and the atrioventricular valves snaps shut = first heart sound
  • Marks the start of the systole
  • Aortic valves remains close
  • Short period (during this phase, ventricles contract but ventricular volume remains constant because heart valves are closed)
• • Ventricular Ejection:
  • Aortic pressure is higher than ventricular pressure for most of the cardiac cycle.
  • As the ventricles contract, ventricular pressure increases.
  • When ventricular pressure exceeds aortic pressure, the aortic valve opens, and blood is ejected forcefully into the aorta.
  • Once ventricular pressure falls below aortic pressure, the aortic valve closes, creating the second heart sound (S2).
  • The closure of the aortic valve causes a small dip in aortic pressure, known as the dicrotic notch, which marks the end of ventricular ejection.