Which chamber of the heart has the thickest wall and why?
The order of thickness of the heart wall from thin to thick is auricles, right ventricle and left ventricle.
Both auricles are with comparatively thin walls. Because both auricles receive blood from vena cava and pulmonary veins.
From right auricle blood enters right ventricle. Right ventricle is with thick wall. This is because the blood is to be circulated in lungs and is to bring back from lungs.
Left auricle receives blood from lungs. The left ventricle is with thickest walls. This is because from left ventricle blood is squeezed through literally thousands of kilometers of blood vessels. (In adult person of 60 kg. is with approximately 25,000 kilometers of blood vessels)