47 unknown cards.
11 unseen hearts

There are 47*23=1081 possible unknown hands
and there are 11*5=55 suited heart hands, so
naively, it would be 55 of 1081 -- so roughly 1 in 20.

Now, pairs are obviously not suited, and, otherwise suited hands are preferable to unsuited ones, and, there's no real notion of how your opponent plays, so you'll have to go from there.