The first several weeks after surgery there is about a 30% to 40% chance of getting AF, but it usually goes away by itself, and if not, they will do a cardioversion. This is because the heart is all inflamed, not to mention the fact that it is remodeling.
The AF (and probably the VT) you have now are most certainly caused by your valve disease, so even if you have it a while after surgery, chances are it will go away eventually.
However, for the AF, you might ask whether you need a Maze Procedure. I had one, and I had only had AF for a small amount of time before the surgery.