Guys how would you feel/react if a girl from your past contacted you?

Guys how would you feel or react if a girl who you used to like contacted you, after a longtime of not being in contact? This would be a girl you liked however nothing actually happened between you two even though both of you knew you liked each other.

Would your reaction depend on why you didn't stay in contact or would you just be happy to hear from her?

If you have any experience of this happening please share, I would like to hear about it