Four cases of longitudinal dissociation of the atrioventricular node, with dual pathways developing during the acute phase of an inferior wall myocardial infarction (three cases) or during acute ischemia (one case), are presented. In all four cases, two grossly different P-R intervals were recorded, and in two cases, studies of the His bundle confirmed the location of the dissociation within the atrioventrcular node. In one case, premature atrial depolarization caused a bidirectional shifting of P-R intervals, while in the remaining three cases, premature ventricular depolarization (spontaneous or pacemaker-induced) was responsible for this phenomenon. In all cases, evidence of longitudinal dissociation of the atrioventricular node appeared during the acute phase of the infarction or ischemia, and in all of them the phenomenon was transient. This favors the assumption that this phenomenon is of a functional nature, most probably related to the ischemic lesion of the atrioventricular node.