heckit with a probit

Hi

I have data for voting behaviour on two (related) binary votes. I want
to examine the second vote, running separate regressions for groups
who voted different ways on the first vote. As the votes are not
independent, I guess that there is an issue with selection bias.

So, I think I would like to fit a heckit style model but with a binary
dependent variable - so, in effect, two successive probits. Is there a
way to do it in R? (Alternatively: am I thinking about this the right
way?)

Cheers
David