The Northern Ireland international previously spent four years at Rangers between 2008 and 2012 and has been heavily linked with a return to his former club for most of the summer.
Lafferty has scored 20 goals in 51 appearances for Hearts since joining them from Norwich last term, but now looks set to depart the club after just a season.
Rangers' first approach back in July was rejected out of hand, but a compromise has now been reached and the 30-year-old undergo a medical on Wednesday afternoon.
'Gers' boss Steven Gerrard is thought to be hopeful of concluding a deal in time for Lafferty to be available for Thursday's Europa League play-off against Ufa.