The FDA is studying whether bisphosphonates cause irregular heart rhythms, and so far the results are good. While some research had indicated more such problems for those taking Fosamax and Reclast than for those on a placebo, the FDA has not found a causal relationship and says the concern is not a reason to discontinue the medication. The agency will continue to examine the issue, however, for another year.
Here's an article on the subject: http://www.chron.com/disp/story.mpl/ap/fn/5179214.html

