Thirty patients with electrocardiographic evidence of bilateral bundle branch block (BBBB) underwent 36 surgical procedures. Despite an 83 percent incidence of significant cardiac disease, the overall mortality was 10 percent. In no case was death attributable to complete heart block, though one patient was found at postmortem to have suffered acute myocardial infarction. Patients with previous syncopal episodes showed no increased incidence of arrhythmias and no patient had a documented Stokes-Adams attack. It would appear that the routine use of temporary cardiac pacemakers is not justified in the preoperative patient with presumed BBBB. However, since the factors that ultimately cause complete heart block are not known in patients with BBBB, constant cardiac monitoring is mandatory in the intraoperative and immediate postoperative period.