Why is the ventricle of the frogs heart thicker than the atria

The ventricles of the frog are thicker than the atria because the ventricles have to pump blood to more important areas of the frog's body. The atrium shows less resistance to the flow of blood hence they do not need as thicker walls as the ventricles. The heart of a frog has one ventricle and two atria. Hence, this single ventricle should be powerful enough to pump blood to the important parts of the body.