Abstract: AIM: To study the effects of various extracellular Ca²⁺ concentration and amiloride on 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 INa-Ca was recorded using whole-cell patch clamp technique with a declining ramp pulse protocol. RESULTS: Amiloride can block the INa-Ca significantly. At potential of +50 mV, amiloride 10^-5, 3×10^-5 and 10^-4 mol.L^-1 inhibited the I_Na-Ca by 15.4%, 22.6% and 40.9%, respectively; at potential of -80 mV amiloride inhibited I_Na-Ca by　5.6%, 14.6% and 23.2%, respectively. CONCLUSION: Intracellular Na⁺-overload can activate Na⁺-Ca²⁺ exchange system which can be affected by extracellular Ca²⁺. Amiloride can block I_Na-Ca in guinea pig ventricular myocytes. Its inhibition effects on outward currents were greater than those on inward currents.