Atrial fibrillation(At) is very common disease with increased prevalence with age.With rapid aging of population,prevalence is rapidly increasing.In my institution,prevalence of Af was reported 5.4％ in 65-69 years old,6.4％ in 70-74 years old,7.5％ in 75-79 years old,9％ over 80 years old,which is somewhat lower than that of western countries.