And you know the answer....
My heart, if it stops beating, I'm done!!!!!
It's a trick question, many of our organs are vital and the lack of just 1 is certain death.
It's kinda like a couple bickering, claiming that they're more important when the truth is that both of them are just as important and wouldn't live well by themselves.
My brain. When it stops I will be gone forever.
My heart... it control how hard I work.