Rob Kearney, Gordon D'Arcy, Luke Fitzgerald and Ryan Jones are the other Lions tourists who feature in the two squads for what promises to be one of the top games of the weekend in Europe. Brian O'Driscoll misses out through injury.
"It adds a bit more banter, I suppose, at the bottom of a ruck," admitted Leinster skipper Heaslip to the Irish Times
"I didn't play in the Ospreys (Pro12) game but I was "waterboying" the life out of it on the sideline and got chatting away to a couple of them and they were in good form. I was slightly jealous that I wasn't back playing and they were.
"But I suppose you learn little things about how they go about their business. You always learn more playing with a guy than playing against him. So you pick up a couple of things of how they go about their business.
"I respected "Tips" (Tipuric) a lot before from having played against him but even more so after playing with him. The guy is an absolute workhorse and he's a nightmare around the breakdown.
"He's great when he's on your team. But he's going to be a massive challenge for us, as well as the rest of them. But you just learn a lot more about players, and you get a lot more respect for them."