Background— Atrial fibrillation (AF) is the most common cardiac dysrhythmia and a source of considerable morbidity and mortality, but lifetime risk for AF has not been estimated.

Methods and Results— We included all participants in the Framingham Heart Study who were free of AF at index ages of 40 years and older. We estimated lifetime risks for AF (including atrial flutter) to age 95 years, with death free of AF as a competing event. We followed 3999 men and 4726 women from 1968 to 1999 (176 166 person-years); 936 participants had development of AF and 2621 died without prior AF. At age 40 years, lifetime risks for AF were 26.0% (95% CI, 24.0% to 27.0%) for men and 23.0% (21.0% to 24.0%) for women. Lifetime risks did not change substantially with increasing index age despite decreasing remaining years of life because AF incidence rose rapidly with advancing age. At age 80 years, lifetime risks for AF were 22.7% (20.1% to 24.1%) in men and 21.6% (19.3% to 22.7%) in women. In further analyses, counting only those who had development of AF without prior or concurrent congestive heart failure or myocardial infarction, lifetime risks for AF were approximately 16%.

Conclusions— Lifetime risks for development of AF are 1 in 4 for men and women 40 years of age and older. Lifetime risks for AF are high (1 in 6), even in the absence of antecedent congestive heart failure or myocardial infarction. These substantial lifetime risks underscore the major public health burden posed by AF and the need for further investigation into predisposing conditions, preventive strategies, and more effective therapies.