Twenty-two of 31 patients with right bundle-branch block (RBBB) following acute myocardial infarction died. Right bundle branch block was present on admission in 21 cases and subsequently appeared in ten cases. Ten of 14 patients (72%) with RBBB and left anterior hemiblock died of a cardiac arrhythmia. Of the 11 patients with RBBB and left posterior hemiblock, seven died of a cardiac arrhythmia and one died of pulmonary emboli (73%, total mortality). Three (60%) of five patients with RBBB died—two with an arrhythmia and one in shock. The one patient with RBBB and prolonged PR interval died of a cardiac arrhythmia.