The Dutch defender, who only moved to Craven Cottage from Everton during the January transfer window, was left frustrated after the Cottagers crashed to a 3-1 defeat at fellow strugglers Cardiff City on Saturday in what had been billed as a relegation six-pointer.
The result leaves Felix Magath's men rooted to the foot of the table, four points adrift of safety with only nine games remaining this season.
And while Heitinga feels it will be a tall order to avoid dropping into the Championship, he is refusing to give up until it is mathematically impossible.
He said: "You have to believe we can still do it. I still believe in the miracle. There are still 27 points to fight for, and we play some of the teams around us, but to stay in the Premier League now would be like winning the Champions League for us.
"Survival for us is the trophy. It's the same now as winning a cup or a title. The only thing that matters at the moment is Fulham. It does not matter how we survive, we have to find a way.
"The manager afterwards said to us that Fulham is a club full of history and we have to try everything to keep it in the league. But it needs to be quick, because it is already five minutes past midnight now."