I guess there can be all kinds of T waves, each of them meaning some specific condition either temporary or permanent. Without any more info. from your doctor, I would believe what he says. The heart goes through many changes after surgery. Time usually takes care of them.
If you're worried, give your doc a call and pin him down on what specifically he sees.
But for the most part, you should believe what you yourself are feeling. If you have any kind of funny feelings which haven't been explained, don't be shy about asking.
Best wishes to you.