Background and Objectives It has been suggested that prolongation of the QRS duration (>120 ms) is an independent risk factor for mortality in patients with cardiomyopathy. The purpose of this study was to examine the association between QRS duration and survival in patients with heart failure. Methods We performed a retrospective analysis to examine the association between QRS prolongation (≥120 ms) and mortality. The study population included 669 patients with heart failure. Two groups, on the basis of baseline QRS duration <120 milliseconds or ≥120 milliseconds, were identified. The groups were compared with respect to total mortality and sudden death. Subgroups were also stratified by right bundle branch block and left bundle branch block, ejection fraction (EF) <30% and ≥30% to 40%, ischemic and nonischemic cardiomyopathy, amiodarone and placebo. Results Prolonged QRS was associated with a significant increase in mortality (49.3% vs 34.0%, P = .0001) and sudden death (24.8% vs 17.4%, P = .0004). Left bundle branch block was associated with worse survival (P = .006) but not sudden death. In patients with an EF <30%, QRS prolongation continued to be associated with a significant increase in mortality (51.6% vs 41.1%, P = .01) and sudden death (28.8% vs 21.1%, P = .02). In those with an EF of 30% to 40%, QRS prolongation was associated with a significant increase in mortality (42.7% vs 23.3%, P = .0036) but not in sudden death (13.3% vs 12.0%, P = .625). After adjustment for baseline variables, independent predictors of mortality were found to be prolongation of QRS (P = .0028, risk ratio 1.46) and depressed EF (P = .0001, risk ratio 0.965). Age, type of cardiomyopathy, and drug treatment group were not predictive of mortality. Conclusion QRS prolongation is an independent predictor of both increased total mortality and sudden death in patients with heart failure. (Am Heart J 2002;143:1085-91.)