I think the USDA Database - which is the carb counter we have under Low-Carb Tools at the top of the page - is very accurate for nutrition counts.

Here it is, for 1 cup of heavy whipping cream:

Total Carbohydrates 6.64 g
Dietary Fiber 0.00 g
Total Protein 4.88 g
Total Calories 820.58
Total Fat 88.06 g

Karen