In a family of 14, five members presented conduction defects including atrio-ventricular block (2), right bundle branch block (3), and left anterior hemiblock (3). Another sibling who died suddenly at the age of 30, exhibited normal electrocardiograms, whereas no information was available on the remaining two.A review of the literature suggests a familial character of the disease with an autosomal dominant mode of inheritance. It also suggests a progressive widening of the QRS complex with advancing age and the occurrence of left bundle branch block or left anterior hemiblock as precursors of atrio-ventricular block.