Hello there, go ahead and ease your mind, I went through the same thing last week, I have a right branch bundle block, and from what I understand it is a electical problem with your heart, but it does not effect blood flow, as far as the nuclear stress test, i had that done yesterday, and its not hard, you walk on a treadmill and when you reach your target heart rate they inject this radioactive fluid in your I.V. and then you wait 45 minutes and they take pictures of your heart, its not painful, but I got a metal taste in my mouth after it, but I think you will be ok, just talk to your doctor and get a better understanding of what is going on, and be glad that they are taking precaution before surgery.