Since losing almost 45 pounds, I've joined a gym and am now trying to increase my cardiovascular fitness. I had a scare last year with a tentative finding of pulmonary hypertension, which has yet not been proved nor ruled out. However, since losing all the weight, I'm no longer having shortness of breath when I exercise.
Anyway, I can't seem to increase my endurance on the elliptical. 20 min is the most I can do, and I'm dying after that.