Beta Blocker Tolerance

I started taking Toprol XL 25 mg once daily for arrythmias and noticed immediate improvement. After several months, arrhythmias seemed to increase so I consulted my internist and slowly titrated the dose upward to 50 mg q day.  After several more months, I noticed my arrhythmias increasing again so titrated the dose to 100 mg TWICE daily.  This gave me excellent PVC free days and nights - for  a while!  Now I have PVCs all the time, haven't backed the dose down, still taking 100 mg of Toprol XL twice a day - My question is - can you build a tolerance to a cardio-selective beta blocker like metoprolol?  I see no other explanation why my arrhythmias continue to increase on such a high dose of this medication.  ?????  Thanks!

[Barbarella]

Because PVC's or as listed as "uneven heartbeats" is one of the side effects for "some" people taking Toprol.  Sometimes these drugs make the PVC's worst, sometimes right away, sometimes later on,