I was sitting at the computer typing on Friday when my pacemaker started shocking me around the implant device area and my pulse started racing. I felt terrible, head pounding, and drove to the doctor's office. They checked my pacemaker and said that my pulse shot up to 226 beats per minute and that my pacemaker was set to shock it back down if it went over 125. I have been having tachycardia for seven months and am on Nadolol 40 mg but this isn't stopping these episodes of racing heartbeat that occur every three to four weeks. I started having racing heartrate and had it for seven months before I got this pacemaker because I was told after wearing a holter monitor for a week that sometimes my heart was slowing down to a dangerous level. What is wrong with me? How can I have tachycardia and bradycardia alternating like this? Has anyone heard of this before?