Pulmonary vein
The pulmonary veins provide a supply of oxygenated blood from the right lung to the left atrium of the heart. This is the only example in the human body where a vein will transport oxygenated blood rather than deoxygenated blood. The pulmonary veins as well as the pulmonary arteries are major components of the pulmonary circulation. This pulmonary circulation is an essential part of the cardiovascular system of the body[1].