Heart rate rhythms have been demonstrated to parallel specific psychological processes. Efficient experimental control of the amplitude of these rhythms would allow evaluation of bidirectional psychophysiological hypotheses. This experiment was performed to examine the specificity of the heart rate rhythm response to oscillatory head-up tilt. Seventy-one adults (36 male, 35 female) aged 18-30 were positioned on a tilt-table and oscillated at 0.08 Hz with a maximum tilt angle of +21 degrees for a 10-min period. Heart period, heart period variability at 0.08 Hz (i.e., Traube-Hering-Mayer (THM) variance), and respiratory sinus arrhythmia (quantified using vagal tone, V) were measured. For a subset of 21 subjects, continuous measures were derived to examine the response to onset of oscillatory tilt. Respiratory activity was also measured in these subjects. There was a significant increase in the amplitude of the THM variance during tilt stimulation. Tilt did not significantly change heart period, V, or respiration frequency. Following cessation of tilt, THM variance returned to baseline levels, heart period lengthened for males, and V increased for both sexes. Subjects with higher amplitude baseline V were characterized by more rapid THM variance response to tilt. Results suggest that parasympathetic tone moderates the THM variance increase elicited by low-frequency oscillatory tilt.