The larger chambers of the heartThe chambers of the heart are the main drivers within an intricate pathway, delivering blood to the lungs for gas exchange and enriching the body's cells with oxygen. The contracting and relaxing chambers facilitate varying pressure gradients that drive a... (3 times the volume and muscle thickness than the atriaRight and left atria (1/3 volume and muscle mass of the ventricles) pump blood to the ventricles. Chambers and Layers of the Heart 1. Six Second ECG Guidebook (2012), T Barill, p. 190), responsible for the pumping of blood to the lungs and the rest of the body.