So the Irishmen should know what it takes to reach the showpiece final and Heaslip has called for a big defensive display on Friday night against the third highest try scorers in the Guinness PRO12.
"They've got a back line that's playing some really good rugby right now - they've got some good finishers," he said.
"They're going to be a tough side to contain, but we'll back our system, back our 'D'.
"When it comes to this end of the competition, I've been lucky to have a bit of experience in it, it's usually defence that wins championships.
"They've got the second best defence in the competition; they've got the third highest try-scoring ability; that's two pretty potent stats to have."
Leinster finished the regular season top of the league but suffered a 30-6 defeat at the hands of their semi-final opponents in the penultimate round.
Ulster went on to beat Ospreys 46-26 in Swansea while Leinster recovered to score 50 points against Benetton Treviso in the final game of the regular season.
Despite their recovery, Heaslip admits their disappointing defeat at the Kingspan Stadium is still on the players' minds ahead of Friday's semi-final.
"When you live it the way we live it, you have to wear your heart on your sleeve, on your jersey. It's not just you you're representing; it's your family, your friends," he added.
"That weighs heavy on you when you feel like - not for the lack of effort, I don't think there's ever a question of a lack of effort, but just a lack of execution - because you take such pride in it you can feel a little deflated after a game like the last time we played Ulster.
"The great think about sport is, more often than not, there's always another opportunity, another crack at it.
"We've got an opportunity to wear that jersey with pride in front of a sold out crowd on Friday."
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