I'm a 31-year-old male, in reasonably good shape, with no history of heart disease in my family. About 12 days ago, I began to suffer from a rapid heartbeat; perhaps the best way to describe it is feeling as if I'd just done some light exercise - moving boxes around the basement or something. It was there when I woke up, and it would flare up periodically throughout the day, without anything to precipitate it.