Vagal stimulation and cardiac chronotropy in rats.

Increasing frequencies of electrical stimulation of the right vagus nerve in the rat yielded a progressive lengthening of heart periods. Stimulation was capable of driving vagal control of cardiac chronotropy over its full physiological dynamic range, to the point of sinus block. The steady-state transfer function between vagal stimulation frequency and cardiac chronotropy was approximately linear, with a slope of 7.4 ms/Hz. The linearity of the stimulation-heart period function is consistent with previous reports in dogs, rabbits and humans, although the slope of the function was considerably lower in the rat.