Cardiac Cycle

Ventricular Contraction

  • Goal: Pump blood out of ventricles.
  • Blood moves through semilunar valves to aorta or pulmonary artery.
  • Pressure is high in ventricles, low in blood vessels.
  • Atrioventricular valve closes, semilunar valve opens.

Ventricular Relaxation

  • Pressure in ventricles is low, atrium pressure is high.
  • Blood flows from high pressure (atria) to low pressure (ventricles).
  • Atrioventricular valves open, semilunar valves close.
  • Blood flows from high to low pressure.
  • Valves don't open simultaneously; defects cause heart murmurs.

Heart Sounds

  • Result from vibrations in ventricular and blood vessel walls.
  • Lub: AV valves (tricuspid & bicuspid) closing (S1).
  • Dub: Semilunar valves (aortic & pulmonary) closing (S2).
  • S3 & S4 are abnormal sounds.
  • Heart murmur: Turbulent sound due to defective valve.

Cardiac Cycle

  • Sequence of events showing blood flow through chambers.
  • Diastole: Relaxation.
  • Systole: Contraction.
  • Both heart sides work simultaneously.

Cardiac Cycle Phases

Ventricular Filling (Diastole)

  • Ventricles fill with blood in diastole (relaxation).
  • Right atrium has high pressure, ventricles have low pressure.
  • Atrioventricular valve opens, semilunar valves close.
  • Atrial systole occurs (atria contracts) to squeeze remaining blood into ventricles via SA node excitation

Isovolumetric Contraction (Systole)

  • Volume remains constant; ventricles contract.
  • Pressure increases, closing atrioventricular valves (S1 - "lub" sound).
  • Semilunar valves already closed.
  • End diastolic volume: Amount of blood in ventricles after filling.
  • Atrial diastole begins.

Ventricular Ejection Phase (Systole)

  • Pressure higher than other chambers; blood ejects into aorta and pulmonary artery.
  • Semilunar valves open; atrioventricular valves remain closed.
  • Atrial diastole continues.

Isovolumetric Relaxation Phase (Diastole)

  • Ventricles begin to relax (ventricular diastole).
  • AV valves remain closed; atrial diastole continues.
  • Semilunar valves close (S2 - "dub" sound).
  • End systolic volume: Blood left after ventricular ejection.
  • Cycle repeats, starting with ventricular filling.