The cycle of contraction of the heart
This is another quite large animation which will start to move continuously when it has fully loaded.
Note the valves - shown in blue - which control the direction of blood flow. Those between the atria and venticles (atrioventricular valves) are supported by tendons attached to the walls of the ventricles. The other valves (semilunar valves) allow blood to leave the heart - either to the lungs or the rest of the body.
As the animation starts, the atria fill, then contract (atrial systole), pumping blood via the atrioventricular valves into the ventricles. Then the venticles contract (ventricular systole), causing the atrioventricular valves to shut and the semicircular valves to open, allowing blood out of the heart.
Note the function of the tendons preventing the atrioventricular valves from turning inside-out. This is followed by relaxation (diastole) of the ventricles, and the semilunar valves shut. The cycles then repeats itself.
