Background Some studies have confirmed that the right ventricular walls of most rodents, such as canines and humans, have evident transient outward potassium current (lto1) heterogeneity, and this heterogeneity is closely related to J point elevation, J wave formation, and some ventricular tachycardias such as ventricular fibrillations caused by Brugada syndrome. This study is designed to investigate transmural electrical heterogeneity of the canine right ventricle during repolarization (phase 1) from the viewpoint of 4-aminopyridine sensitive and calcium-independent lto1.Methods Adult canine single right ventricular epicardial (Epi) cells, mid-myocardial (M) cells, and endocardial (Endo) cells were enzymatically dissociated. Whole cell voltage-clamp recordings were made to compare the lto1 values of the three cell types.Results At 37℃ and using 0.2 Hz and + 70 mV depolarizing test potentials, the average peak lto1 values of Epi cells and M cells averaged (4070±1720) pA and (3540±1840) pA, respectively. The activated and inactivated Epi and M cells kinetic processes were in accordance with the Boltzmann distribution. Compared with lto1 in Epi cells and M cells, the average peak lto1 in Endo cells was very low, averaged (470±130) pA.Conclusions These results suggest that there are evident differences and potent gradients in lto1 between the three cardiac cell types, especially between Epi and Endo cells. These differences are among the prominent manifestations of right ventricular electrical heterogeneity, and may form an important ionic basis and prerequisite for some malignant arrhythmias in the right ventricle, including those arising from Brugada syndrome and other diseases.