Abstract: AIM: To explore the effects of brucine on transient outward potassium current (Ito) of ventricular cardiomyocytes of rats. METHODS: Single ventricular myocytes of rats were obtained by enzymatic dissociation. The whole-cell patch-clamp recording technique was used to record the changes of Ito by different dosages of brucine. RESULTS: Brucine significantly reduced Ito in a concentration-dependent manner. Brucine at 5 μmol/L shifted the stabilized activation curve to the right and the half-point of actiation potential (V1/2) from ( 30.7±10.2) mV to ( 27.8±5.8) mV (n=8, P<0.05). Brucine (5 μmol/L) shifted the stabilized deactivation curve to the left and the half-point of actiation potential (V1/2) from (41.6±1.0) mV to (75.0±2.8) mV (n=8, P<0.05). Brucine (5 μmol/L) significantly prolonged the recovery time. CONCLUSION: Brucine has significant inhibitive effects on Ito, which may be one of the mechanisms that underlie its antiarrhythmic effect.