I know its very dissapointing, but its better to be safe than sorry. If there is a underlinning heart condition, it doesn't mean you won't be able to have the surgery, but that they will need to take special precautions. But from the surgeons point of view, they need to know what they are dealing with...I think your doctor made a good call.
When after my surgery the first thing the surgeon told me was " don't take any more blood pressure meds"...I had had a few very low reads during surgery and he said they weren't needed any more. I had lost weight before my surgery and probably didn't need to be taking them anymore.
Had you lost weight before surgery? It might have been enough that you need to have the dosage adjusted.