The present invention provides a method of stimulating an excitable tissue (e.g., in vitro, in vivo) with a primary electrical stimulus through a primary electrode at a primary stimulation frequency, to produce a propagating action potential in the excitable tissue. The invention is carried out by concurrently stimulating the excitable tissue with a secondary electrical stimulus through at least one secondary electrode at a secondary stimulation frequency. The primary and secondary stimulation frequencies are preferably different from one another. The secondary electrical stimulus preferably has an amplitude not more than one third that of the primary electrical stimulus. Preferably, propagation of the action potential in the excitable tissue is enhanced (e.g., when propagation of action potentials in the tissue is otherwise unstable, partially blocked, or fully blocked). Apparatus for carrying out the method is also described.
