It pumps blood. Yups. Well, for most of history, people were unsure what the heart's main function was. Even Leonardo Da Vinci gave up studying it and he's probably one of the five smartest guys ever. Even now, it's not as easy as it should be to find out how the ticker works. But we're lucky, this Ted-Ed animation will explain it to you perfectly.
[youtube]http://www.youtube.com/watch?v=ruM4Xxhx32U&sns=em[/youtube]