What if Kairi's heart interacted with Ventus's heart while Sora had her heart within his own? After all, Ventus was(and currently still is) residing within Sora's heart from the time Birth by Sleep ended.

It's likely, but we'll never know.

namine?well she does have blond hair....kairi doesn't...........i have no clue.

Interesting.  That's possible.

Possible. If they did, why didn't Kairi tell Sora at all? Unless the memory was bleached from her head. Or hearts don't receive memories by themselves. Anyway, there are like 15 people's hearts in Sora's. Who knows what's going on in there?

I've pondered that myself for a while now. They could have unknowingly interacted seeing as how Ven's heart was asleep and Kairi probably didn't understand what was going on well. It'd be interesting if this becomes a factor later on but right now there's so little behind the theory all we can do is wait and see.