Cream consists of milkfat and some milk solids. The milkfat is a fat, not a protien. None the less, cream contains cassein, a protien found in milk. This can cause the cream to break if heated too much, or combined with an acidic ingredient. But just as milk can be combined with acidic cheese, and heated and stirred to form a homogeneous sauce, without breaking, so to can the heavy cream. Heating it won't cause it to sour. But it can cause it to break if not done properly. Just as in milk, the protiens found in cream will clump together (break). Please see the link: Cooking Tips: Cream
As for your your dish developing an off taste, there are sugars in cream as well. The sugars and protiens can and will stick to the bottom of the pan and scorch. This will give you an off flavor. Gently heating you dish will make it pleasantly hot to eat, without ruining the flavor.
My recommendation, the microwave is your freind. If you don't want to use a microwave, then heat over low heat, stirring frequently, or heat in a double boiler, as was suggested previously in this thread.
Also remember that herbs and spices will continue to give out their flavors as time continues. The flavors also become better dispersed within the dish. This could also be a factor in the final flavor of you dish.
Hope these ideas help.
Seeeeeya; Goodweed of the North