equivalent code in c# for excel
 

I have a VBA macro which changes the pivot table summation caption, the code
is as follows:
ActiveSheet.PivotTables("OpenPivTable").PivotField s("Sum of OldName"). _
Caption = "new Name"
what is the equivalent code in c#? I am creating pivot tables in VS 2003
using c# and want to the above, any help will be appreciated.