Conclusions1. It is possible to obtain electrograms on the isolated perfused dog's ventricular septum, and these show a reproducible pattern. 2. The records indicate that the excitatory process in these experiments traveled in a complicated fashion and the pattern varied somewhat from animal to animal. In some of the experiments the excitatory pathways varied over a period of time. As a basic rule, the left side of the septum was found to be activated early and the upper right side late. 3. The apparent absence of septal electromotive forces in electrocardiograms recorded by usual clinical methods, which has been explained by neutralization of potentials spreading inward from each side, is not supported by these preliminary observations on the isolated septum.