Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

The ongoing sequence of contraction (systole) and relaxation (diastole) of the heart.

Question 2

Describe ventricular diastole and atrial systole.

Answer 2

• Ventricles relax
• Atria contract, decreasing volume and increasing pressure of chamber
• This pushes blood into the ventricles and causes a slight increase in ventricular pressure and chamber volume because the ventricles are receiving blood

Question 3

Describe ventricular systole and atrial diastole.

Answer 3

• Atria relax
• Ventricles contract, decreasing volume and increasing pressure of chambers
• AV valves shut (pressure higher in ventricle than atria) to prevent back-flow
• Pressure higher in ventricles than aorta or pulmonary artery, forcing open SL valves

Question 4

Describe cardiac diastole.

Answer 4

• Ventricles and atria relax
• High pressure in pulmonary artery and aorta closes SL valves to prevent back-flow
• Blood returns to heart and atria fill again due to high pressure in vena cava and pulmonary veins
• Starts to increase pressure in atria
• Blood flows passively into ventricles from atria because ventricle pressure falls below pressure in atria, opening AV valves.