In the last five years, increasing evidence has emerged for a genetic predisposition to atrial fibrillation (AF). Framingham Heart Study investigators observed that the odds of developing AF were three times higher for individuals with at least one parent in whom AF was diagnosed before the age of 75 than in those without a parental history of AF. Similarly, in a large group of Icelanders, the risk of developing AF was increased nearly five-fold if one parent was affected before the age of 60. Furthermore, single rare genetic variants thought to be responsible for familial AF have been identified.