In humans, which chamber of the heart receives oxygen-rich blood from the lungs first?

Oxygenated blood returning from the lungs travels through the pulmonary veins and enters the left atrium of the heart. From there, it passes through the bicuspid (mitral) valve into the left ventricle, which pumps it into the aorta for systemic circulation. The right atrium receives deoxygenated blood from the body via the venae cavae. Hence the chamber that first receives oxygen-rich blood from the lungs is the left atrium.