Oh yeah, under 50 and paced. And de-fibed. Sports with a pacemaker can take getting used to, and some adjustments to the pacemaker settings.
I gave up bird hunting-can't hit the broad side of a barn anyway, and I've always bruised with a shotgun. Now I don't want to bruise more with the coumadin. But the dogs do the fetching for the hunting buddies, and mostly we just retriever train anyway. Guns are generally unloaded training props. I'm not required to shoot a gun in AKC tests, and I'll just skip the UKC tests. The training involves hiking over cow pastures--it can be rough some days, I'll grant you that.
I also run agility, and the sprinting with a fast dog is a bit of a bother. I tend to run out of air (run 175 yards while twisting, turning, waving your arms and hollering commands at the dog--try it, you'll like it) because my top end HR is just lower than I'd like. But so is my V-tach (starts about 180) so I'm stuck with a top end HR of 155.
My EP says to tap on the pacer a bit before I start, to get the heart rate up.
I have my responsiveness set just one setting below "teenager" and it seems to work for me pretty well.
I'd say you have more problems with the backpack on the pacer and wires than the functionality issue. Do be careful with the leads.