['Atrial fibrillation (AF) has been reported to be associated with decreased survival in population-based studies. Its prognostic importance in end-stage heart failure is not clear.', 'We investigated the prognostic implications of AF as function of left ventricular (LV) ejection fraction (EF) in 8,931 consecutive patients undergoing echocardiography at our medical center between 1990 and 1999. Patient characteristics were: age 66 +/- 13 years, EF 51 +/- 15, AF in 1,203 patients. There were 1,911 deaths over a mean follow up of 913 days. The prevalence of AF was 11% in patients with normal left ventricular ejection fraction (LVEF) (EF >/= 55%, n = 5, 130), and 18% each in those with mild (EF 41-54%, n = 1209), moderate (EF 26-40%, n = 1183) and severe reductions in left ventricular ejection fraction (LVEF) (EF </= 25%, n = 961). The 5-year survival rate was 72% for those in sinus rhythm compared to 56% for those in AF (p < 0.0001). The effect of AF on 5-year survival was most pronounced in those with normal LVEF (62 vs 78%, p < 0.0001) followed by those with mild reduction in LVEF (57 vs 72%, p = 0.02). It was not a predictor of survival in those with moderate (5-year survival 55 vs 61%, p = ns) or severe LV dysfunction (5-year survival 47 vs 45%, p = ns). Using the Cox regression model, AF was an independent predictor of mortality after correcting for age and LVEF in the entire cohort and in those with normal LVEF, but not in those with reduced LVEF. Among the other co-morbidities analyzed, an independent effect of AF on mortality was present in those with QTc >/= 450, raising a possibility of enhanced susceptibility of these patients.'] Is prognostic significance of atrial fibrillation a function of left ventricular ejection fraction?