Final Answer:
During late ventricular relaxation, the atria and ventricles relax; atria continue passively filling with blood; atrioventricular valves open, and ventricles begin to passively fill; semilunar valves remain closed.
Step-by-step explanation:
Atria and Ventricles Relax: Late ventricular relaxation, known as diastole, involves the relaxation of both the atria and ventricles. This phase allows the heart chambers to recover and prepare for the next cardiac cycle.
Atria Continue Passively Filling: As the atria relax, blood continues to flow passively into them from the veins. This passive filling is facilitated by the higher pressure in the veins compared to the atria.
Atrioventricular Valves Open: The atrioventricular valves (tricuspid and bicuspid/mitral valves) open during late ventricular relaxation, allowing blood to flow from the atria into the ventricles.
Semilunar Valves Remain Closed: The semilunar valves (aortic and pulmonary valves) remain closed during this phase, preventing the backflow of blood from the arteries into the ventricles.