Blood first enters the atria by the veins. The walls of the atria contract, pushing blood from the atria into the ventricles through the atrioventricular valves, which are open at that time. The semilunar valves are therefore closed, so that the ventricles can fill with blood. The walls of the ventricles then contract powerfully and the blood pressure rapidly rises inside them. This first causes the atrioventricular valves to close in order to prevent back-flow of blood to the atria and then causes the semilunar valves to open, allowing blood to be pumped out into the arteries. At the same time this is occurring, the atria start to refill with blood collected from the veins. The ventricles stop contracting and as pressure falls inside them the semilunar valves close, preventing back-flow of blood from the arteries to the ventricles. When the ventricular pressure drops below the atrial pressure, the atrioventricular valves open. Blood entering the atrium from the vains then flows on to start filling the ventricles once again.
Steam-Heart's happened in 9801.
Heart of Africa happened in 1985.
Flyable Heart happened in 2009.
Carnage Heart happened in 1995.
Black Heart happened in 1991.
Clover Heart's happened in 2003.
Heart of China happened in 1991.
Bionic Heart happened in 2009.
Heart of the Alien happened in 1994.
Prism Heart happened in 2000.
Arcana Heart happened in 2006.
The Gas Heart happened in 1923.