The "retired cardio" is probably from the ole school of thought that physical exercise should be avoided for heart patients.

It is true GTN reduces the heart's afterload by relaxing arteries and widen vessels thereby reducing blood volume and this decreases the amount of blood returned to the heart with the end result of less oxygen needed to meet the heart's demand.

Unfortunately, there can develop nitrate tolerance that may require an increase in dosage for the same results. I take isosorbide (slow release of NO) for a period of time and discontinue for a short period. I have used sublingual nitro (fast activation) if and when angina develops...rarely need, no side effects.