To analyze the coherence between neuronal discharges (ND) in the rostral ventrolateral medulla (RVLM) and the cardiovascular activity, we observed the neuronal discharge in RVLM responding to electric stimulation of the defense area of the mid-brain. Fast Fourier transform (FFT) was performed to analyze the coherence between the signals of ND and blood pressure to determine if the ND were cardiac rhythmic. The coherence between ND variability (NDV) and heart rate variability (HRV) was also analyzed. The results showed: (1) majority of the neurons (67%) were excited responding to electric stimulation in the defense area of the mid-brain; (2) the electric activity of about 70% of the neurons were substantially inhibited by administration of phenylephrine; (3) 64% of the neurons were actively synchronous with cardiac cycle; and (4) significant coherence between NDV and HRV in HF component was shown in a half of the neurons (50%). The coherence analysis thus provides a new tool to investigate the regulation of the autonomic nervous system.