A patient is described with complete heart block and a ventricular septal defect, both secondary to a stab wound of the chest. The escape rhythm was characterized by a wide QRS interval with a configuration suggesting right bundle branch block. His bundle (H) recordings revealed "split" H potentials with a P-H1 interval of 100 msec and an H2-V interval of 40 msec. Recording of left bundle branch (LB) potentials showed the left bundle branch spike to occur in the H2-V interval with an H2-LB interval of 15 msec and an LB-V interval of 25 msec. Atrial pacing produced prolongation of P-H1, administration of atropine and isoproterenol produced shortening. Wenckebach periods proximal to H1 were noted at an atrial paced rate of 190/min. During the study, the QRS pattern unexpectedly shifted from right to left bundle branch block, with H2 potentials still preceding each QRS interval. The most likely explanation for this was the occurrence of longitudinal dissociation in the distal His bundle allowing preferential distribution of the cardiac impulse to one or the other ventricle. However, the possibility of varying bundle branch block, or shifting of the pacemaker from the His bundle to the bundle branches could not be absolutely excluded. In summary, His bundle recording suggested a site of block in the His bundle. Observations are made on the nature of "split" H potentials and evidence for the occurrence of longitudinal dissociation in the His bundle is presented.