AQA/EDEXCEL/OCR A Level Biology – Cardiac Cycle Graph Explained

Between points A and B - atrial systole
● Atria contract → atrial pressure
Point B - beginning of ventricular systole
increases
● Ventricles begin to contract →
● Ventricles are relaxed
ventricular pressure increases
● AV valves open
● Ventricular pressure > atrial
● Blood is forced into ventricles
pressure
● Ventricular volume and pressure
● AV valves close
increase slightly




Point C - ventricular systole
● Ventricles continue contracting
● Ventricular pressure > aortic
pressure
Point A - end of diastole ● Semilunar valves open
● Ventricles are relaxed ● Blood is forced into the aorta
● AV valves are open ● Ventricular volume decreases
● Atria begin to contract
● Blood is forced into the ventricles