The pulmonary veins are blood vessels that carry oxygen-rich blood from the lungs to the heart. There are four main pulmonary veins, two from each lung, which enter the left atrium of the heart. This process is essential for delivering oxygen to the body, as the heart pumps this oxygenated blood to various tissues. These veins are unique because they are the only veins in the body that carry oxygenated blood. In contrast, most veins carry deoxygenated blood back to the heart. The proper functioning of the pulmonary veins is crucial for maintaining effective circulation and overall health.