The heart is an incredible pump. Weighing only about as much as one of your sneakers, a heart beats over two billion times in an average lifetime, pushing a river of blood that carries nutrients and axygen through sixty thousand miles of capillaries to every cell in the body. In stunning photos that will amaze you with their beauty, you can watch while blood cells defeat invading bacteria and see how tiny platelets form blood clots. This journey is as wonderful as any voyage to the stars.