Double Heart Beat

I was just told by my doctor that what was causing my heart to flutter and race was that I had a double heart beat where there is normally one. She said that this was normal in some people and not to worry about it unless the fluttering or racing starts and won't quit. What I can't remember is the medical term that she used for this dx.
I also just found out that my grandfather, and two aunts have this too.

Does anyone have any information that I could read about this condition?

Thanks,

pebbles