The walls of ventricles are much thicker than atria. Explain. 

Explanation

The structre of heart of fishes,reptiles,birds and mammals show many structure of evolutinoary significance.Thiker walls of ventricles is one of them
Ventricles have thickes walls because these are mainly involved in pumpuing the blood to the body parts with certain pressure.
The walls of the left ventrivcle is about 3 times thicker from the right ventricle,while the atria acts as a collecting chambers for the blood which is starting to the heart thus have thin walled.Also they have to force the blood into the ventricles that lies just below there thus atria have thin walls.