[ ABSTRACT] AIM:To screen out a suitable lead for monitoring the ambulatory electrocardiogram ( ECG) in un-restrained toad, and to investigate its practicability.METHODS:After subcutaneously implanting the electrodes in toads under anaesthesia, the ambulatory ECG of 5 leads were monitored with BL-420S data acquisition and analysis system, and the leads which could well express the waveform in ECG were screened out.The recovery process of the toads from the arti-ficial hibernation within 6 h, the day-to-day stability of the heart rate ( HR) and the heart rate variability ( HRV) in 5 suc-cessive days of hibernation, and the HR and HRV after freeze-thawing process were monitored to determine its practicabili-ty.RESULTS:Two out of 5 leads showed better ECG waveforms.Compared with 6 h post hibernation, lowered HR at 0 h and 1 h was observed, and the standard deviation of normal R-R intervals ( SDNN) was significantly increased ( P<0.05 or P<0.01), but the HR and SDNN from 2 to 5 h showed no significant difference, suggesting that the cardiac function reached the steady state after 2 h recovery.The HR at 2 h and 4 h on day 4 and day 5 decreased significantly compared with that on day 1 (P<0.05 or P<0.01), followed with a significant increase in SDNN (P<0.05 or P<0.01), sugges-ting that the ECG remained stable within 3 d.The HR increased, while SDNN decreased significantly at 1 h and 12 h post-thawing compared with that at pre-freeze (P<0.05), indicating the damaged cardiac function after freeze-thawing process. CONCLUSION:The method of subcutaneously implanting electrodes is suitable for effectively monitoring the ambulatory ECG in toads.