Beginning with all chambers of the heart in the "relaxed" phase, describe the ca

i.   The heart begins with all chambers relaxed. The AV valves are open and the semilunar valves are closed. Low pressure in the heart causes the blood to flow passively into the atria and ventricles.
ii.   The atria contract. The ventricles are relaxed. Additional blood flows into the ventricles. Semilunar valves are closed. AV valves are open.
iii.   The ventricles contract. The atria relax. The AV valves close. The semilunar valves are still closed. Pressure rises within the ventricles.
iv.   High pressure within the ventricles causes the semilunar valves to open. Blood is ejected from the ventricles into circulation.
v.   The ventricles relax. The atria are still in diastole. The semilunar valves close. Pressure is low in the atria and ventricles.
vi.   The low pressure allows blood from circulation to flow into the atria and ventricles, and the cycle begins anew.