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Four brothers with a maximum age difference of 20 years, the eldest of whom has been re-examined after a 10 year interval, have sinoatrial block, a supra-hisian atrioventricular block and paroxysmal atrial arrhythmias which have led to partial atrial standstill in the eldest: left anterior hemiblock is also present in the two youngest brothers. The condition is very well tolerated. This family is compared to the other 12 reported cases of familial idiopathic binodal block in the adult, an autosomal dominant condition with variable penetration. The diagnosis is reserved and justifies endocavitary investigation of the sinus node function and atrioventricular conduction in the four brothers and the most exposed members of their family. The mechanism of the condition is unknown. It seems to arise from variable degrees of nonspecific of the nodal and atrial tissues.

An oriental family with over 265 living descendants of a polygamous ancestor known to have had a slow pulse and syncopes was studied. Many examples of conduction defects, mainly right bundle branch block, left anterior hemiblock, bifascicular block and artioventricular block were detected. The transmission of the genetic defect was autosomal dominant, the incidence 43%, the penetration very variable, apparently affecting the male descendants predominantly, the expression probably congenital, but with complete heart block presenting at 75 years of age in one case. The localisation of the conduction defect is discussed: the distal extremity of the His bundle after the origin of part or all of the left posterior fascicle. This study, in its clinical and epidemiological context, demonstrates an inherited disease with both typical and "forme fruste" expressions. Compared with other series, it suggests the diverse nature of hereditary and familial conduction defects.