Dead-end tract of the conduction axis.

In the definitive heart the anterior continuation of the main conduction axis is considered to be the right bundle branch. In this study three hearts from neonates and infants were examined in which this situation did not pertain. The conduction axis continued beyond the point of origin of the right bundle branch as a dead-end tract. In two normal hearts the tract then faded out in the central fibrous body. In one heart with Fallot's tetralogy it disappeared on the crest of the trabecular septum. Although we are unaware of any functional significance of these tracts, our findings are of considerable interest in understanding the development of the atrioventricular conduction system.