This study compared monophasic 100-μs pulses with high-frequency electroporation (HF-EP) bursts using an in vivo animal model. Myocardial damage was evaluated by histologic analysis. Compared with 10 monophasic pulses, 20 bursts of HF-EP at 100 and 150 kHz were associated with less damage. However, when the number of HF-EP bursts was increased to 60, myocardial damage was comparable to that of the monophasic group. HF-EP protocols were associated with attenuated collateral muscle contractions. This study shows that HF-EP is feasible and effective and that pulse frequency has a significant effect on extent of ablation.