Pumping Cycle

The sturcture of the heart allows blood to move through the circulatory system in only one direction.
Your heart muscle will pump for more than 2 billion times during your lifetime.
Blood enters the heart's right and left atria from the VEINS ( A blood vessel that carries the blood back to the heart ).

When the atria begins to pump or squeeze the right and left ventricles are relaxed and are not pumping. These chambers receive blood from the atria.

Source: http://www.ihcworld.com/histowiki/fetch.php?w=&h=&cache=cache&media=heart_diastole.png

Then, the ventricles start to pump blood into two large

ARTERIES (A blood vessel that carries blood back to the heart leading to the body and lungs) .
When the venticles are pumping the atria are relaxed.Blood returning from the body enters the atria and the entire pumping cycle begins again.

Source: http://www.mountnittany.org/assets/images/krames/106422.jpg

How do the ventricles receive blood?