Heart failure (HF) and atrial fibrillation (AF) are cardiovascular diseases that have a continuously increasing prevelance and both often coexist. The presence of AF in HF patients has been reported as being between 10 and 50% depending on the different study settings. AF patients have a different clinical profile: they are older, with more severe HF and comorbidities than those without AF. Despite this poor clinical profile, observational studies report a lower use of the recommended treatments such as angiotensin-converting enzyme inhibitors and β-blockers. Clinical trials using antiarrhythmic drugs for rhythm control have failed to demonstrate the clinical advantage of a rhythm control approach over one for rate control. The prognostic role of AF in HF remains controversial, while the impact of new AF has been shown to be associated with an adverse outcome.