Diltiazem
"Started this medication over a year ago, and it has helped keep my heartbeat regular.  I had an episode where my heart rate was over 200bpm, and had to go to the ER in an ambulance from my doctor's office.  It has not repeated, thank goodness, and I had no side effects from this medication, which I take with Zestril (which I'd been taking for many years before)."