Exercise and Bronchiectasis

My pulmonologist has talked about exercise as almost as important as airway clearance in our disease. I'm 77. I also have hfpef which is a form of heart failure. I walk usually everyday or every other day about 30 to 40 minutes. I sometimes bike ride or workout on water (pedal or paddleboard) instead of walking (or waterwalk if its really hot!!)
I tend to have a more steady experience in walking and my pulse is recorded anywhere between 70 and 90's. My resting pulse is anywhere between 55-58. I do try to push myself sometimes but have to be careful at the beginning of my exercise as I can develop distressing shortness of breath (due to the hfpef). However, once i get going, I"m fine. I guess what I"m looking for is, if I"m not getting my heart rate up to my Target Rate as defined by the formula for that, am I ok with what I am doing? I sometimes for a short period of time get my pulse up higher with my bike riding and pedalboarding.