Depending on the lab and the doctors performing the procedure, there ARE some repairs that can be done right there during the cath. It's real specific to what they find and what they can do with the limited access, but there are some small things that can be done such as placing a stent for a blocked artery...
It really depends on what they find, what they're looking for.
Most cases though, I think it's unlikely they'd do any more than look around and see what's really going on.
The cath allows you to actually see the insides of the heart, what the valves and other structures look like, where blood is flowing, what kinds of pressures are where...
They'll use what they find along with the results of all the other testing they might do to plan the best "attack" to treat your condition. They generally use it as a diagnostic tool, not for treatment.