Abstract The effects of divalent cations on resting potential and excitability of myocardial cells were studied. Increasing the external divalent cation concentration (Ca 2+, Sr 2+, Ba 2+) produced an increase in membrane resistance and a depolarization of resting potential with Ba 2+ ions. Action potentials showed a shortened duration when Ca 2+ concentration was increased, and longer duration when Sr 2+ or Ba 2+ concentration was increased. In Ca 2+ free solutions the actions of Sr 2+ and Ba 2+ ions on action potentials durations are more accentuated. Voltage clamp experiments showed that Ca 2+, Sr 2+ and Ba 2+ ions increased the amplitude of slow inward current and modified the kinetics of slow inward current inactivation and delayed outward current activation. These changes could explain modifications of the action potentials.