The maximal normal difference in oxygen content between structures is as follows: The pulmonary artery and right ventricle: 0.5 mL / dL (0.5 vol%) The right ventricle and right atrium: 0.9 mL / dL (0.9 vol%) The right atrium and superior vena cava: 1.9 mL / dL (1.9 vol%) If the blood oxygen content in a chamber exceeds that of the more proximal chamber by more than these values, a left-to-right shunt at that level is probable.