We describe three infants <3 months of age seen consecutively with dilated cardiomyopathy who presented initially with left bundle branch block on the surface 12-lead electrocardiogram. Each infant subsequently had a poor outcome: two died and one required heart transplantation. These results suggest that the presence of left bundle branch block on the 12-lead electrocardiogram conveys a poor prognosis in infants with dilated cardiomyopathy.