Ventricular fibrillation (VF) in dogs is characterized by a rapid increase in its dominant frequency during the 1st minute of reperfusion followed by its decrease during the 2nd minute of reperfusion. The longer is ischemia in VF, the greater is the increase in dominant VF frequency during reperfusion. The 1st minute of reperfusion is characterized by a 1.2-fold increase in dominant VF frequency after 1-min ischemia in VF, by 1.4-fold increase after 2-min ischemia, by 2-fold increase after 3 min, and by 2.6-fold increase after 4-min ischemia. During the 2nd minute of reperfusion, the dominant VF frequency decreased by 1.1-1.3 times, and during 3rd-10th minutes of reperfusion, the dominant VF frequency is stabilized. © Springer Science+Business Media, LLC, part of Springer Nature 2024.