The study describes the electrophysiological effects of transvenous cardiac nerve stimulation in an animal model of myocardial infarction. In ten sheep with recent myocardial infarction, transvenous stimulation of parasympathetic cardiac nerves was achieved from a catheter in the right pulmonary artery. The effects of transvenous cardiac nerve stimulation on sinus rhythm cycle length, ventricular refractory periods and inducibility of monomorphic ventricular tachycardia were evaluated. Sinus rhythm cycle length increased from 620 +/- 24 ms to 723 +/- 30 ms during nerve stimulation with 20 Hz and to 779 +/- 28 ms during stimulation with 40 Hz (p < 0.05). Effective ventricular refractory periods from stimulation sites in non-infarcted right and left ventricular myocardium showed a tendency towards prolongation during cardiac nerve stimulation with shortening after cessation of stimulation. These differences, however, were not significant. In contrast, refractory periods from stimulation sites within the infarcted area remained unchanged during cardiac nerve stimulation. The inducibility of monomorphic ventricular tachycardia by programmed electrical stimulation was reduced during transvenous cardiac nerve stimulation. Pathological examination showed cholinergic nerves in close proximity to the tip of the stimulation catheter in the right pulmonary artery. Transvenous cardiac nerve stimulation in sheep with remote myocardial infarction exhibits electrophysiological effects on the ventricles. Although a parasympathetic effect on the ventricles could not be proven, the observed effects may result from direct stimulation of efferent parasympathetic nerves.