34Heart CirculationMedium1 markWhich statement correctly describes an event in the cardiac cycle that occurs immediately after atrial systole?AA wave of excitation passes through the sinoatrial node (SAN), before spreading down to the base of the septum.BElectrical impulses pass from the muscles of the atria to the muscles of the ventricles to cause ventricular systole.CElectrical impulses pass through conducting fibres, which cause a delay before spreading to Purkyne tissue.DThe semilunar valves close to prevent the backflow of blood.Grade answerSolutionGrading criteria