3 Billion Beats

Mammal's hearts will all beat about a billion times in their life. So a mouse that lives around 4 years will have a faster heart rate then an elephant that lives for 70. But they will both get their billion heart beats in. Except for humans. We have learned to alter our lifespans to the degree that we will get 3x that number. Each of us getting 3,000,000,000 beats should we live to our potential.

Liver: the Salamander Organ

Did you know that if you cut a chunk of your liver off, it will regrow? Most people learn this in grade school, but it's easy to forget until you stop to think about how awesome it really is. Your liver will regrow itself. You can cut off up to 85% and it will still grow back. You could cut off more but you'd die of liver failure before it has a chance to regrow. Which, by the way, only takes a couple of weeks. Right now, you could cut yourself open, saw off a chunk of liver and in less than a month you'll be good as new (assuming you took care not to give yourself an infection in the process). No other body part can do that.