AZ - I personally do not have a pacemaker. However, my father-in-law has had one for about 3 years now. He has slowed down a bit - he's 68, but last year we went to Montana and hunted at about 7000 feet and as long as we paced ourselves he was fine. I've hunted with him for about 12 years now and he's still just as eager to get out there and get that big one as ever! I'd think if you are going to the gym and working out, you will be fine on your elk hunts as long as you realize your limits and stop to catch your breath if needed.
Good luck on that getting that Bull!!!