Now, what about our veins? Well, just like arteries come in different sizes, veins also come in different sizes. The smallest vein is called a Venuel and the largest vein in our body is called the vena cava. We have two, we have the inferior and the superior vena cava. Now, if our arteries actually carry blood away from the heart, then the veins always carry blood to the heart and away from the cells, the tissues and organs of our body. Most of the time, veins carry deoxygenated blood, but sometimes in the case of the left and the right pulmonary vein, they actually carry oxygenated blood to the left atrium of our heart.