Adenosine
"Heart ramped up to 200 bpm. Received two doses of adenosine in ambulance as first dose didn't work.  EMT's warned me it would cause some pretty unpleasant feelings.  Intense burning and pressure occurred instantaneously, from my head to my toes.  It was pretty horrific, but short lived.  I even manged to joke how excited I was to receive a second dose and experience it again. Heart rate was in upper 90's by time I was settled in emergency room at the hospital."