OBJECTIVE This study was undertaken to assess the effects of ropivacaine on the membrane action potential and the voltage-dependent L-type calcium channel current ( I(Ca)) in guinea-pig single ventricular myocytes. METHODS Single ventricular myocytes were prepared by enzymatic dispersion. Whole-cell current and voltage-clamp techniques were used to monitor membrane potentials and I(Ca). RESULTS Ropivacaine (10(-5) and 10(-4) M) reduced the overshoot and shortened the duration of the action potential. Hyperpolarization of the resting membrane potential was observed in the presence of ropivacaine (10(-4) M). Ropivacaine (10(-5)-10(-3) M) reduced I(Ca) dose-dependently and reversibly, and the 50% inhibitory concentration (IC(50)) of ropivacaine was estimated as 4.3 x 10(-4) M. Furthermore, the inhibition of I(Ca) was not a use-dependent block. CONCLUSIONS Ropivacaine has an inhibitory effect on I(Ca) in the guinea-pig single ventricular myocyte. It is concluded that the mild negative inotropic effect induced by ropivacaine can be attributed in part to shortening of the duration of the action potential, which is caused by inhibition of I(Ca).