Beta Blockers and Exercise

I have recently been put on a low dosage beta bloker for rapid heart rate. My question is, is this going to make my exercise less effective? My pulse when exercising, typically gets to 170-180, but with the beta blocker, it stays between 150 and 160. Should I just exercise a bit longer to get the same results?

That's a question for your cardiologist.  I find that beta blockers make me feel really sluggish and my heart rate drops so low I find it hard to do anything.  Some people don't feel it, but I do.  Everybody is different.