Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. Pulmonary veins are a major source of ectopic activities initiating the arrhythmia and the fibrillatory conduction, associating multiple wavelets and high frequency functional reentries called "rotors". AF is responsible for atrial electrophysiological, contractile and structural remodelling, shortening the wavelength, accelerating AF cycle length and sustaining the arrhythmia. A better understanding of the mechanisms responsible for this arrhythmia led to new therapeutic approaches, including ablation, and could eventually lead to the development of new anti-arrhythmic drug agents.