Abstract: AIM　To study whether KB-R7943 has selective inhibitory effect on the inward and outward Na⁺-Ca²⁺ exchange current (I_Na-Ca) in guinea pig ventricular myocytes. METHODS　Through setting up the model of intracellular Na⁺-overload during myocardial ischemia and reperfusion, the current-voltage relationship of I_Na-Ca was recorded using whole-cell patch clamp technique under bi-directional ionic conditions. RESULTS Currents were elicited by a declining ramp pulse depolarized immediately from holding potential of -40 mV to +60 mV, then repolarized to -100 mV at a speed of 80 mV·s^-1 and returned to the holding potential under bi-directional ionic conditions, while the ［Na⁺］ was 25 mmol·L^-1 in the pipette solution. The currents increased time-dependently and voltage-dependently which reached from (2.51±0.15) pA·pF^-1 to (5.94±0.13) pA·pF^-1 at +50 mV and from (-1.92±0.13) pA·pF^-1 to (-3.17±0.16) pA·pF^-1 at -80 mV (n=12) after 3 min and there is no significant run-down of the current. KB-R7943 10-6 mol·L^-1 was found to decrease the current to (4.62±0.05) pA·pF^-1 by 29.4% at +50 mV and to (-2.30±0.18) pA·pF^-1 by 22.1% at -80 mV (n=5) after 5 min. While 10^-5 mol·L^-1 KB-R7943 was shown to decrease the current to (3.13±0.03) pA·pF^-1 by 61.7% at +50 mV and to (-1.62±0.03) pA·pF^-1 by 56.9% at -80 mV (n=7). CONCLUSION　KB-R7943 can block I_Na-Ca in guinea pig ventricular myocytes. But, it did not show selective inhibition effect on inward and outward currents.