First of all it depends if it is a prereq class or not. If it is, many will require you to take it again, yes, but some will not (you will have to call the school to see for sure, or perhaps your pre-med advisor might have some specific info on the schools you're considering.) If it isn't a prereq, no, you don't have to retake the class.
I have a C- in a pre-req class, and I haven't heard of anything about having to retake it. (though I might have to retake it anyway to raise my GPA if I don't get in this year)
