By the time you finish reading these words, your heart may have beaten up to 50 times. As you walk, eat, and sleep, your heart continually pumps trillions of blood cells through thousands of miles of blood vessels inside your body. You may not be able to see your own heart, but all you have to do is look inside this book to see how this amazing organ works. Acclaimed science writer Seymour Simon has teamed up with the Smithsonian Institution on a new edition of this indispensable guide that takes you through the heart, from atrium to capillary and back again.