Can a heartrate quickly and dramatically change during surgery?

So, we're catching up on old episodes of Lost last night, and Jack is doing surgery where he's patching up an artery he nicked (silly Jack) -- while he was "fixing" it the heartrate jumped from a dangerous 206 to a "normal" 120 in about a second. Does that really happen? And why? Does the body suddenly say, "Ok, everything is fine! Back to normal!"?