Night and day, whether you're asleep or awake, your heart is always beating. Read and find out how your heart works and how to keep it healthy.

Paul Showers wrote twenty books for the Let's-Read-and-Find-Out Science series, including favorites such as What Happens to a Hamburger? and Where Does the Garbage Go? Mr. Showers worked on the Detroit Free Press, the New York Herald Tribune, and for thirty years, the Sunday New York Times.