What actually happens when your heart goes lub-dub, lub-dub, lub-dub? Where does blood enter your heart? How exactly does it move through the heart and get to the different parts of your body? What are veins and arteries? And how does all this work with your lungs and digestive system? Every minute of every day, your blood is working its way all around your body, keeping you alive! Find out how, and so much more, in Circulation of the Blood.