This article explores the potential of third-order statistics to analysis of heart rate variability (HRV) signal. Bispectral analysis of short-term HRV signals, obtained from a group of of healthy subjects under various experimental settings, showed the HRV activity to be located on specific bifrequency regions of the magnitude bispectrum. Nine strength measures were defined and were found to respond selectively to induced perturbation of sympathetic-vagal control of heart rate. In general the measures contained the spectral information and provided complementary information.