Affecting around 1% of the general population, the rate of atrial fibrillation (AF) rises to 9% after the age of 80 years, and probably even higher still over the age of 90. AF originates in the left atrium (LA), whereas typical atrial flutter stems from the right atrium (RA), giving it a characteristic aspect on the ECG. However, both these arrhythmias can occur in the same subject at different times. Among the many clinical manifestations, AF can give rise to a transient ischemic attack or cerebrovascular accident, generally non-syncopal, or on the contrary, may provoke syncope through reduced cardiac output in association with tachyarrhythmia, without neurological signs. AF is a frequent cause of heart failure in elderly subjects.