The actress will bow out from the BBC soap in early 2012 when her current contract reaches its conclusion. Show insiders have promised a "dramatic" departure for Heather.
Fergison has now revealed that she is keen to stay clueless over Heather's final plot for the time being - as she doesn't trust herself to keep the secret under wraps.
"I have to be honest, I was shocked when EastEnders told me they weren't renewing my contract," Fergison told The Sun. "I don't know why they did it. I love playing Heather, but I guess she is like Marmite - people either love her or hate her."
Confirming that she is grateful to the show for giving her five years of work, the 47-year-old continued: "I said to them, 'Thank you for having me and please don't tell me how I go'. I know everyone's going to ask me and I won't be able to keep quiet, so I just want to find out when I get the script. I don't even want to know if I'll be killed or if the door will be left open."
Fergison also spoke of her future plans, explaining that she would love to compete in a future series of Strictly Come Dancing.
"Now I'd like to do other things, maybe some presenting, maybe Strictly," she said. "I think I'd be the Ann Widdecombe of the contest, but there's definitely no harm in trying."
Fergison recently described her time at EastEnders as "wonderful" and a "privilege".
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Watch Heather's EastEnders character trail below: