If you ride with a HRM that has audio signals you could set it to beep at you when you get to a certain HR. I have mine set up this way - both to beep if I get too high and if I get too low. I usually only use it this way for the first half of a long (century+) ride. That way I make sure I'm working hard enough, but not too hard.

When my HR gets too high on a climb I sort of soft pedal, usually that's enough to bring it back down. If it doesn't, I may slow my cadence or downshift, if I still have anything to go down to. Sometimes I may decide that it's all right to be a beat or two over and I'll ride with it beeping but not put out any more effort.

I'd probably go get a check up since you have had some heart issues in the past. Just for peace of mind.

V.