York South Weston is suppose to be a tight race between the NDP and Liberals. The NDP won the seat by a narrow margin in a by-election in February 2007. In a general election held later that year the Liberals took the seat back but by a slim of margin.
http://en.wikipedia.org/wiki/York_South%E2%80%94Weston_(provincial_electoral_district)
The NDP now hold the seat federally having taken