Atrial fibrillation (AF) is common in the intensive care unit (ICU) and is particularly frequent (46%) in septic shock patients. Inflammation favours AF in the general population, and there is a growing body of evidence that inflammation also plays a role in AF occurring after cardiac surgery but also in the general ICU. How such a finding could modify the therapeutic approach remains elusive. The impact of AF on mortality is not clearly demonstrated in the ICU, with AF reflecting essentially the severity of the underlying disease.