This review focuses on the relation between atrial fibrillation (AF) and atrial natriuretic peptide (ANP). ANP is produced by the atria secondary to atrial stretch. By causing atrial stretch, acute AF leads to an increase in plasma ANP concentration, which serves to normalize haemodynamics through natriuresis and vasodilation. However, data have been reported suggesting that prolonged AF, by inflicting structural atrial damage, is associated with a reduced capacity by the atria to produce ANP. An inverse relation was thus demonstrated between the duration of AF and plasma ANP concentration. In addition, a reduced ANP response to exercise has been shown to be predictive of unsuccessful cardioversion of AF to sinus rhythm. Finally, ANP has also been shown to predict outcome after a maze operation. Outcome was poor when preoperative plasma ANP concentration was low. Moreover, a high atrial collagen content, as a measure of atrial degeneration, correlated with low ANP. These data indicate that ANP may serve as a marker of atrial integrity, which may help in selecting AF patients for therapeutic interventions.