ABSTRACT
<p><b>OBJECTIVE</b>To observe the effect of vagal stimulation of different frequencies on heart rate and heart rate variability in the toads.</p><p><b>METHODS</b>The animals were prepared to be models of isolated heart with right vagosympathetic trunks, then the nerves stimulated by different frequencies. Collected the electrocardiogram of isolated hearts and analyzed the data with HRV software.</p><p><b>RESULTS</b>Since the effect of sympathetic nerve had been diminished, vagal stimulation resulted in HR being markedly attenuated (P < 0.01), SDNN and RMSSD being significantly increased (P < 0.01). There was no significant difference in different levels of frequency. Contrast to group control, HR,SDNN and RMSSD each changed clearly. At the frequency of 0.2 Hz, HF increased markedly (P < 0.01), and LF/HF decreased obviously (P < 0.05) in group P + P. While at the frequency of 0.8 Hz, HF and LF/HF were both around the level of pre-stimulation.</p><p><b>CONCLUSION</b>These findings suggest that in the certain electrical stimulation frequency range, the effect of vagal on HR increases along with the frequency. Without the effect of sympathetic nerve, the modulation of vagal to HR and HRV may have different ways.</p>