Simplify the following text for a Grade 9 native English-speaking person.
Original: When the lower chambers are filled and the valves to the atria are closed , they then contract in the second more important time phase , sending blood out of the heart to the body from the left ventricle and to the lungs from the right ventricle as seen in the diagram to the right .
Simplified: Blood is pumped out of the heart to the body from the left ventricle and to the lungs from the right ventricle as seen in the diagram to the right .