Why is the left side of the heart bigger than the right and what is the role of the avn in the heart?

The left ventricle is responsible to bump the blood through the body, and the right ventricle is responsible for the blood circulation in lungs, the size of them is determined by the resistance of the blood flow through which they have to pump. Body parts have much more resistance and need more pressure to pump through than lungs. Thus they are more muscular. 

Explanation:

1,12,2,18,3,15,4,21,5,11,6,13