Hi DT:
I asked the same question of my doctor, who said I would probably not be able to get my heart rate up to 80% of my max heart rate. I always understood that you needed to be at this level to derive any aerobic benefit from exercising, but that isn't necessarily the case. As long as you maintain a moderate level of intensity, you will benefit from the work-out (cardiac-wise). So yes, the beta blocker will reduce your ability to increase your HR (you'll fatigue before HR reaches a high range), but no, it won't negatively impact the cardiac benefits. Hope this helps.