Which of the following statements concerning the cardiac cycle is true?

A) Blood enters the right and left atria only during diastole.
B) Most ventricular filling occurs before the atria contract.
C) During ventricular systole, the AV valves open.
D) The semilunar valves remain closed throughout ventricular systole.
E) Most of end-diastolic volume comes from active filling.

Cardiac Cycle

refers to the sequence of events that occur in the heart during one beat, including the contraction (systole) and relaxation (diastole) periods.

Diastole

The phase of the heart cycle when the heart muscle relaxes and allows the chambers to fill with blood.

Ventricular Filling

The phase of the cardiac cycle in which the ventricles fill with blood, following diastole and before systole.