Atrial fibrillation (AF) represents one of the most important comorbidities in patients with heart failure (HF). This report highlights the available evidence for the relationship between AF and cardiac resynchronisation therapy (CRT). Studies on the use of CRT in patients with HF and AF have demonstrated its effectiveness. It seems to reduce the AF burden and determines left atrial reverse remodelling. No definite data are available on AF ablation in patients with CRT but it might represent a therapeutic option. Furthermore, modern implantable pacemakers and cardioverter-defibrillators are provided with diagnostic algorithms which allow a better understanding of the AF burden.