At stake is a trip to the Heineken Cup final in Cardiff on Saturday, 21 May, and the clash between Saints' Soane Tonga'uiha and Perpignan skipper Nicolas Mas in the scrum is going to be one of the highlights of the game.
"The French pride themselves on their scrummaging and Perpignan gave us a bit of a lesson out there in the Heineken Cup last season. They got a penalty try against us and that still hurts," admitted Hartley.
"But we have moved on from that and learned from it. The emphasis for us this season has been on every single scrum.
"We've learned that you have to hammer the opposition every time you go down in a scrum. It is no good having four or five good scrums and then letting things slip.
"Your work rate has to be high and it has to be better than the other team. I'm lucky that I have two such great props around me."
Mas will have England international Perry Freshwater, twice a winner of the Heineken Cup with Leicester Tigers, and the French replacement hooker Guilhem Guirado, packing down with him in the Perpignan front row, while Hartley with have Tonga'uiha and Springbok tight head Brain Mujati supporting him.
"They are like two gentle giants Soane and Brian - my cornerstones with me in the middle to whip them. They go about their work and they epitomise what we are about," added Hartley.
"This group of players has developed and grown together, but we haven't got a final yet. The worry is that if we don't win something soon the chance might slip."