Fantastic day - 70, sunny, wind less than 10 mph. I had time for only 16 miles, but I learned something yesterday that really helped today (and will help in the future). I had to go in to my doc's office to get my pacemaker read and adjusted; some stuff can't be done via wifi and phone. I asked what a-fib they saw, and they said 'none'. I pulled out my phone and showed a number of rides during which I had some events that look a lot like a-fib.
The tech said that was due to a sensor in the pacer. It senses increased activity, so it bumps the HR to pump enough blood to keep me from keeling over. The HR bump (it usually jumps from about 100 bpm to 165 bpm in a moment) is normal. I can push myself harder than I've been doing, as long as I don't get any symptoms like shortness of breath. I'm so glad I asked - it was really worrying me.
I did, in fact, push myself harder on this ride, and I rode faster than usual (i.e., what had become usual for me). I averaged just about 2/3 of what I averaged 35 years ago.
But I slow for STOP signs and stop if a car has right-of-way, and I stop at red lights. Sometimes, of course, I stop at red lights to rest, not to respect the law....