If you mean 'stiff' rather than 'heavy', then I would think we are looking at something causing excess friction. I suggest you check your tyre pressures first because it's easy, and if low, will make a noticeable difference. If after that there is no change then I would work look at the steering column bushes. Other possibilities are track rod ends (though they usually work loose rather than seize up) and less likely suspension arm lower ball joints - but again these normally loosen up with age. Your car hasn't by any chance been standing in flood water any time in the last year has it? That might well cause corrosion in the lower ball joints and lead to their seizing - hence stiffness.
Sorry, there is a lot of guesswork there, hope some of it helps, start with the tyres!
Richard, January 2009
