Riddle me this :)(My second riddle post)

Hey everybody poopiteepoop won my last riddle which is right here http://www.sharenator.com/Can_you_solve_this_riddle/ So he/She will receive 50% of this post, but I have a little Easter treat for the person who answers this one if anybody answer’s this one in the next 4 hours I’ll give you 75% of the next riddle post so here is the riddle 🙂

I’m so fast you can’t see me,
Though everyone sees straight through me,
I don’t stop until the day you die.
What am I?

And I’ll give you a hint it’s not a heart so guess again 😛