Conventional electrocardiographie equipment (capacitance-coupled amplification) cannot distinguish between RS-T segment and baseline shifts of the ventricular complex. The so-called RS-T segment displacement is the net difference between the undetermined levels of those components. Using direct-coupled amplification, the absolute changes of baseline and RS-T segment on the surface of the exposed left ventricle during levarterenol administration and during regional ischemia, and release-recovery were studied in dogs. Ten significant patterns of displacement were observed. These permitted clear differentiation of the effects of levarterenol injection and hyperperfusion from those of ischemia. The centers and borders of an ischemic area could be distinguished and the change with prolonged ischemia described. The relationship of these observations to the literature and pertinent studies of intracellular action potentials are discussed.