Malcolm O'Kelly, the St. Mary's College clubman, made his 139th appearance in last weekend's 34-18 victory over the Glasgow Warriors and is level in the province's the all-time caps list alongside retired prop Reggie Corrigan.
Leo Cullen, who started alongside O'Kelly in the second row last weekend, could also make his 100th appearance for the province. Meanwhile, Leinster are boosted by the return after injury of Girvan Dempsey for the trip to south Wales.
Jonathan Sexton, a second half replacement against Glasgow at the RDS, made his first appearance in two months while Horgan, Heaslip and Luke Fitzgerald currently share second place in the league's top try-scoring chart with five touchdowns, two behind Llanelli Scarlets centre Regan King.
Horgan, incidentally, is now in second place in the overall Magners League try-scoring list with 24, five behind record holder Matthew Watkins. In all, Leinster coach Michael Cheika has been able to include 11 Ireland internationals in his squad.
LEINSTER Squad (v Llanelli Scarlets): Forwards (14) - Brian Blaney, Leo Cullen (capt), Keith Gleeson, Cian Healy, Jamie Heaslip, Trevor Hogan, Bernard Jackman, Shane Jennings, Cameron Jowitt, Stephen Keogh, Stephen Knoop, Ollie Le Roux, Malcolm O'Kelly, Stan Wright.
Backs (12) - Michael Berne, Gary Brown, Felipe Contepomi, Girvan Dempsey, Luke Fitzgerald, Shane Horgan, Chris Keane, Rob Kearney, Jonathan Sexton, Christian Warner, Chris Whitaker, Cillian Willis.