I'm 51, male, and was diagnosed a few years ago with HBP.  I take
Ziac, which also slows down the heart.  I do the elliptical trainer
and recumbent bike 3x a week.  I've noticed that if I don't take the
Ziac before I work out, I get in the target heart range faster, and
stay in it longer.  Only after I stop working out do I then take a
Ziac.  

Any downside to doing this?  Usually I take it in the morning before I
go to work, and then I workout around 8:00 or so in the evening.  I
only delay the Ziac on the weekends, when I go workout around noon or
so.