Of 70 patients with cardiomyopathy, nine (13%) had bifascicular block: right bundle branch block with left anterior hemiblock in four, right bundle branch block with left posterior hemiblock in two, and left bundle branch block with left anterior hemiblock in three. Isolated left bundle branch block was present in four, isolated left anterior hemiblock in 13, and isolated left posterior hemiblock in one. No isolated right bundle branch block was found. Five of the patients with bifascicular block were evaluated by His bundle electrocardiography and atrial pacing. Block in the His-Purkinje system (prolonged HV interval) was present in four and atrioventricular conduction (AH interval) was normal in all five. Despite a common prolongation in intraventricular conduction, short term prognosis seems to be favorable since: (1) none had spontaneous progression to more advanced block or experienced Stokes-Adams attacks for an average follow-up period of at least 42 months, and (2) with atrial pacing, one-to-one atrioventricular conduction persisted to rates up to 150/min in all patients with no further prolongation of HV interval.