Well, this is what I have found out about my angina and exercise.
I execise daily for short terms on a stepper (5-10min, 3 or 4 times, intense) and then later on a treadmill. The treadmill is the main exercise and I do sessions of 500m up to about 2.5km once or twice a day.

On the stepper I get virtually no angina (pressure or pain). I find the stepper really useful as I can exercise as much as I like without worrying about the angina barrier. (I think one problem with angina and exercise is that angina can stop a person getting a enough exercise to be really useful - so any recovery becomes a very slow process.)
My Dr says I could also take nitrate while I exercise, but I refuse to do that.

On the treadmill I get pressure (builds gradually), and sometimes pain as well. Of course I stop when I feel it's too risky to continue. My Dr. says to be careful and never to try to break through the angina barrier. Sometimes I reckon I do that - maybe foolishly - I don't know. I often feel the chest pressure in slow waves - peaking and then dropping away. Naively perhaps, I interpret this as blood building, bursting through the artery, then slowing again. I try to stop and avoid that situation but sometimes it happens nevertheless.
If I exercise on the stepper I can now get a good treadmill performance - 2 to 3 km - including about half of that uphill. And I sometimes stop when I want - not just because of the angina pressure. The 2-3km treadmill performance is quite reproducible provided I don't have a break (eg stopping for more than a day). The success on the treadmill carries over to my other activities - by that I mean later in the day I can walk up hills without angina - even 6 or 8 hours after being on the treadmill. As I have said before I interpret that as a dilation of the arteries that lasts at least for several hours. In fact I now know it even lasts overnight (ie a good treadmill performance in the afternoon carries over to the next morning and I can again get 2 or 3 km on the treadmill then.)
But I do have a problem - I play sport on 2 or 3 evenings in the week. This is light aerobic exercise for 2 or 3 hours and I come home quite exhausted. Sometimes I get chest pressure doing it. Well, the day after that my exercise capacity is gone. Yep, I am back to the sort of angina I started with months ago. Treadmill performance has gone and I get angina almost from the start and have to stop at a 200 -500m. That has really got me tossed. I exercise harder and it stuffs me up. And it lasts the whole day - in the evening I am still useless on the treadmill. It could be I am just overdoing it. Or maybe it's my blood chemistry I just don't know. My DR is puzzled too. In spite of all this the very next day (ie after the one bad day) I can again get on the 'mill and run 2 or 3 km.
Exercise helps but if you overdo it - it works against you.
Someone here may have an answer to this.
(My Dr has suggested Monudur isosorbide mononitrate 60mg - this is a sustained release nitrate.)
Thanks for reading this long post.
Beafsteak.

Quote from Beefsteak:

On the stepper I get virtually no angina (pressure or pain). I find the stepper really useful as I can exercise as much as I like without worrying about the angina barrier.

Beefsteak: thanks for sharing all the details...there are a number of points to talk about. I am surprised about the above comment, at least on the surface. I have found more rigorous exercise on the stepper than on the treadmill. I can get to higher BPMs faster on the stepper. So your experience is hard to explain....until, I have thought more about the question I have been researching about resistance training in cardiac rehab.

The crew in charge of my rehab says no for now and recommends against it; looking on line finds the same recommendations although some general comments are being made that says it is ok. The basic reason I can discern from the writing is that resistance training raises blood pressure without necessarily a proportional increase in heart rate. Aerobic training seems to raise heat rate without a proportional increase in blood pressure.

Does this sound reasonable? Perhaps the stepper is more like resistance training and raises your blood pressure but not your heart rate (proportionally)?? Since you are data driven, have you compared corresponding heart rates from stepper vs treadmill (at equivalent time periods)? Might be interesting.

I just saw kenkeith's response and this sounds pretty good and might explain some of the general reluctance to include resistance training in cardiac rehab.

Regading your comment about taking the sustained release nitrate...I am taking that and have discovered conflicting knowledge in the technical community. I experienced TREMENDOUS headaches when I first started on the isosorbide, almost debillitating. This has gradually gone away as my body has "normalized" to the presence of nitrates. I asked if the fact that my headaches have decreased means that the coronary artery dilation has also decreased. RNs in the cardiac rehab program said definitely NO, that the head arteries respond differently to the nitrates than the coronary arteries, and the coronaries are receiving essentially the same dilation. The cardiologist however said the opposite: that decreased headaches meant that the coronary arteries were being dilated less. I tend to believe the cardio.