['Atrial fibrillation (AF) is often present in patients with left ventricular dysfunction who receive an implantable cardioverter-defibrillator (ICD). The purpose of this study was to investigate whether AF is associated with appropriate shocks and cardiovascular mortality in primary prevention ICD patients with left ventricular dysfunction.', 'We included 80 primary prevention ICD patients with left ventricular dysfunction and compared the outcome between patients with a history of AF (n=29) and patients with no history of AF (n=51). The primary endpoint was occurrence of appropriate shocks. Secondary endpoints were: (1) the composite of cardiovascular mortality/appropriate shocks; and (2) inappropriate shocks. During follow-up (median 8 months, range 1-60), patients with a history of AF more often received appropriate shocks than patients with no history of AF (24 vs. 6%, P=0.03). The composite endpoint of cardiovascular mortality/appropriate shocks was also more likely to occur in patients with a history of AF (34 vs. 12%, P=0.02). History of AF predicted appropriate shocks (HR 6.9, 95% CI 1.7-27.5, P=0.006) and the composite endpoint of cardiovascular mortality/appropriate shocks (adjusted HR 5.1, 95% CI 1.7-15.1, P=0.003). There were no differences in occurrence of inappropriate shocks.'] Does atrial fibrillation predict appropriate shocks in primary prevention implantable cardioverter-defibrillator patients?