Several mechanisms have been described for the pathophysiology of AF: focal pulmonary vein triggers, micro- and macro-structural reentry, point source with fibrillatory conduction, fixed or moving functional reentrant rotors, multiple wavelets with functional and structural reentry, 3D structural dissociation and dysregulation of the autonomic nervous system. The development of AF in HF appears to be a multifactorial process. The causative relationship is reciprocal. AF can induce electrical and haemodynamic deterioration and can cause tachycardia-mediated cardiomyopathy resulting in HF. By inducing a rapid ventricular response and altering diastolic function, AF can also cause HF symptoms even in patients with normal left ventricular (LV) systolic function.