The main goal of this research is to evaluate the defibrillation efficacy with the high-frequency waveform on ventricular fibrillation in small animals. A biphasic defibrillator with adjustable frequency was designed for this study. This custom-designed defibrillator can be adjusted to generate four different frequencies of 125, 250, 500, and 1000 Hz. Six rat hearts were induced VT/VF by electrical induction using the waveform of these four frequencies. Success VT/VF-induction by applying those four frequencies were recorded and observed by optical mapping. The results showed that the VT/VF-induction success rate is increasing along with higher frequencies. The VT/VF-induction success rate is 16% in 125Hz and 250 Hz, 33% in 500 Hz, and 100% in 1000 Hz with S1-S2 protocol at 100 ms coupling interval. Also, using optical mapping technique, shock-induced optical potential showed that only high-frequency waveform exhibited the largest tissue responses in the middle position of the heart. In conclusion, high-frequency (1000Hz) defibrillation waveform has the highest defibrillation efficacy comparing to other lower frequencies used in this study.