The answer to that question, at least for me, is over 401 million.  My heart has beaten over 1.8 billion times since my birth, and the total number of candles I've had on my collective birthday cakes is 1,225. 

Just in case you weren't feeling old enough, there's a website that will really make you ready for the rocker on the front porch.  Just input the date of anyone's birth date and you'll be flooded with a myriad of facts that you probably never wanted to know...but you just have to look.

In addition to heartbeats and breaths, you'll also find out how old you were during some of the world's biggest historical events, how far you have traveled through space while on this planet, and other informational nuggets that will cause you to reach for the Geritol.