A system is provided for stimulating one or more cells, wherein the stimulation is sub-threshold and may alter a transmembrane potential of the one or more cells. For some populations of cells it may be possible to affect the transmembrane potential to gain a therapeutic benefit. Cells of the sino-atrial node spontaneously depolarize predominantly due to the slow depolarization of transmembrane potential. The present system may provide sino-atrial cells with a local field stimulation that while not eliciting an action potential may nonetheless alter local transmembrane potential. Such alteration of transmembrane potential may permit an increase or decrease in a rate of depolarization, and hence modify heart rate.
