The impact of right bundle branch block on long-term prognosis after anterior wall myocardial infarction is unclear. In 932 patients with Q wave anterior infarction, the short- and long-term prognostic significance of the presence of right bundle branch block was analyzed. Compared with 754 patients without block, 178 patients with right bundle branch block after myocardial infarction showed an increased incidence of left ventricular failure (72% versus 52%, p less than 0.001) and increased in-hospital (32% versus 8%, p less than 0.001) and 1 year after hospital discharge (17% versus 7%, p less than 0.001) cardiac mortality rates. The presence of right bundle branch block was an independent predictor of increased in-hospital and 1-year mortality when entered in a multivariate analysis. However, the absence of left ventricular failure identified a subgroup of patients with right bundle branch block with low in-hospital (4%) and 1 year postdischarge (5%) cardiac mortality rates comparable with those of patients with neither failure nor right bundle branch block (1.7% and 4.8%, respectively). In the presence of left ventricular failure, patients with associated right bundle branch block had higher in-hospital (43% versus 14%, p less than 0.01) and 1 year postdischarge (24% versus 9%, p less than 0.01) cardiac mortality rates than those of patients with failure but no right bundle branch block. Thus, the presence of right bundle branch block after anterior myocardial infarction is an independent marker of poor prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)