The day before, combine water and yeast in a mixing bowl. Set aside to dissolve, or for five minutes. Add milk, margarine, salt, sugar, flour, and oats. Mix until smooth. Cover and allow to set overnight. The next day, fold in egg whites and baking soda. Batter will be thin. Heat a standard waffle iron and spray with cooking spray. Pour enough batter onto hot waffle iron, or filling two-tirds of the waffle iron. Bake for four minutes, or as directed from your waffle iron instructions. After slighlty cooling waffles, use a 3 1/4" heart shaped cookie cutter and cut each waffle into a heart shape.