How does the oxygenated blood reach the heart?

The deoxygenated blood is carried to the lungs by the pulmonary arteries for gaseous exchange. After this, the oxygenated blood returns to the heart through the pulmonary veins. 

The pulmonary veins empty the oxygen-rich blood into the left atrium. Blood flows into the left ventricle from the left atrium. The left ventricle sends blood to the aorta, which distributes oxygenated blood throughout the body.