Atrial fibrillation has been variously described as rebellious palpitations, delirium cordis, and pulsus irregularis perpetuus. The first electrocardiographic demonstration of atrial fibrillation was made in 1906. Later reports confirmed the relationship between electrocardiographically documented atrial fibrillation and the clinical disorder of a chronic irregularly irregular pulse. This article provides the prevalence and clinical significance of atrial fibrillation.