Ryan Stevenson has suggested Hearts became complacent in their bid to confirm third place in the Clydesdale Bank Premier League.
Hearts held a 15-point lead over fourth place at one point this season and were considered genuine threats to title-chasing Celtic and Rangers. However, after losses to each half of the Old Firm saw their hopes of a title challenge end, Hearts have recorded one win in their last five games to give Dundee United hope of overhauling their rivals.
Stevenson said: "It looked so easy at one stage that we were definitely going to get there. It's been tough. When you open up that big a gap, you maybe switch off and think we're 12, 15 points in front, we're fine. The gap closes very, very quickly. Dundee United have shown how good a team they are and pressed back."
He added: "We managed to get a little bit of luck on Wednesday night (United lost 2-1 at Motherwell).
"We know that if we go off the boil Dundee United will be right on our tails.
"For us personally we've got to take it every game at a time."
Stevenson has been encouraged by Hearts' displays this season and believes Jim Jefferies' men can put together a more sustained challenge next term.
He added: "This is where Hearts should be. A lot of teams push Rangers and Celtic to January and fade away.
"We've pushed them until March this year and we've only been together as a team for a year.
"We need to finish third, go away and look next season to push on a bit further. We've definitely got the squad and we've definitely got the players to do that."