Trust me, all doctors, be they surgeons, anaesthetists or 'other', have all seen these things before. It's not that uncommon. I've nursed patients with enough conditions to fill a medical text book and they've come through the surgery with flying colours. It's the anaesthetist who'll mostly have to handle this, not the surgeon. And they are specialists in their field. That's also why they use so much monitoring equipment to view almost every vital sign (pulse, blood pressure, respiration, ECG, blood oxygen/carbon dioxide levels, core temperature) so any little change can be picked up on instantly and remedial action taken. This is what you pay him for. A good anaesthetist and his assistant won't leave your side for a moment for the duration of the surgery, not even to go to the bathroom or have a coffee!
So don't see this as a set back. They'll do all sorts of tests so the anaesthetist knows exactly what the state of your heart (and the rest of you!) is and what your normal readings are right now. This will give him a base line to work from so he can more readily spot any variations during the surgery.
Far from freaking out, your surgeon will most likely just say "Oh."!!