Smokin' Joe's answer is not quite as complete as it (maybe) needs to be. Not so much thinking of the OP but of others looking for similar info but with maybe slightly different circumstances ...
The short cage RD will be OK up to a certain number of teeth difference overall ...
Campagnolo 2007-version Chorus short cage RDs (that's what you have) will reliably and safely handle a total of 31T difference, with a 27T max sprocket & a minimum sprocket size of 11T, given a max sprocket difference of 16T, provided the frame and hanger dimensions match Campagnolo's specification.
Before this post is swamped with "my mates got x and y and that works fine" type posts contradicting the above, note the two caveats "reliably and safely" and "provided the frame ...." - Yes, some users have managed to squeeze more range out of these RDs in specific circumstances and some have actually (especially on older frames) not managed to get quite as much range ... but these users are operating outside of the "safe" specification and what works in their particular circumstance may and may not work for the OP.
So - what do the numbers mean?
Total tooth difference is the difference at the chainset (50-34 = 16) plus the difference at the cassette - so in the case of the very common 12-25, that's 13T.
16+13 = 29 is your tooth difference - within the RDs capacity and the total difference at the cassette is less than 16 so you are OK.
In the quest for lower gears, though, you might be tempted to fit one of the recently introduced Campagnolo 12-27 or 12-30T cassettes. 12-27 will be marginal but should be OK given the proviso about frame and hanger spec (you may need to pay attention to chain length - very important) and to the "H" screw adjustment (to get good and correct shifting across the range), the 12-30 you won't be able to use.
Full technical details (including frame and hanger specs which have not changed since 2007, at least) are available in the relevant Campagnolo technical manuals all of which are available at
www.campagnolo.com
HTH
Graeme
Campagnolo main UK SC