Dentify the structure of the human heart which is a large vein (right and left branches) that carries oxygenated blood from the lungs to the left atrium of the heart

The vein being described is pulmonary vein. Veins are blood vessels that carry deoxygenated blood to the heart from all the body parts. However, pulmonary vein carries oxygenated blood from the lungs to the heart, so as to be pumped to the other body tissues through the aorta. It carries oxygenated blood from the lungs into the left atrium where it is returned to systemic circulation.