The heart is a hollow organ divided into two sections. Your right heart
receives oxygen poor blood from your body and pumps it two your lungs where
it picks up oxygen (making it reddish.) Then it comes back to the left heart
where it is pumped through the aorta into the rest of the body. This cycle
continues. Each side of your heart has two sections, the ventricle and the
atrium. The blood always goes from the atrium to the ventricle. The heart
actually pumps twice because of this, through to the lungs and through to
the body. That's why you hear THUMP-THUMP, THUMP-THUMP instead of THUMP,
THUMP.

Arteries generally go to your body and veins go to your heart. The exception
is in the heart area. The blood goes through the arteries to the lungs (body
part) and through the veins to the heart. Heart attacks are caused by your
veins and or arteries (usually arteries) getting clogged up which therefore
doesn't let the blood through.