The left atrium serves as the midway point for newly oygenated blood returning from the lungs to enter once again into the heart. The left atrium is smaller in size and has thicker walls than the right atrium. There are four major pulmonary veins connected to the left atrium that drain oxygenated blood from the lungs and carries it to the heart. These are the only veins in the body that carry oxygenated blood.

HEART TOUR: