Atrial fibrillation is the most common sustained rhythm disturbance, with a heterogeneous presentation, occurring in the presence or absence of detectable heart disease or related symptoms, evolving in paroxysmal, persistent or permanent forms. Prevalence and incidence are mainly depending on age and congestive heart failure. Atrial fibrillation is frequently observed in elderly population. Prognosis can be poor, owing to the risk of embolic events, mainly ischaemic strokes, with a rate of 5% yearly, and to an increased mortality rate, about twice that of persons in normal sinus rhythm. Atrial fibrillation can present as an isolated arrhythmia (20 to 40% of cases) or be associated with an underlying cardiac disease which exerts a main influence on prognosis.