Blocking their way to a final date in Cardiff against Leinster, stand a Perpignan side who have to win to get back into Europe's top competition next season after a disappointing domestic campaign.
"Our team can beat anyone on its day," said Hartley, who started all of England's victorious RBS 6 Nations campaign.
"We need to take our chance now, seize this opportunity.
"We've got a good group of players and if we can keep the group intact we could really achieve something."
Hartley came in for considerable criticism ahead of England's Six Nations opener against Wales, but after an impressive performance at the Millennium Stadium, he is hopeful his reputation is improving.
He also missed out on the last World Cup due to a long suspension for gouging but he insists he is now a different player.
"I think slowly some people might be beginning to look at me in a different light - a less dark one," said the New Zealand-born 25-year-old.
"I have matured. With experience you look at the game differently and realise your actions can affect the team.
"You've got to be seen to be doing the right things, making the correct decisions on the field."