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AIM: To study the effects of tetrahydroacridine (tacrine) on voltage-gated Na+ channels in cardiac tissues.METHODS: Single ventricular myocytes were enzymatically dissociated from adult guinea-pig heart. Voltagedependent Na+ current was recorded using whole cell voltage-clamp technique. RESULTS: (1) Tacrine reversibly inhibited Na+ current with an IC50 value of 120 μmol/L (95 % confidence range: 108-133 μmol/L). (2) The inhibitory effects of tacrine on Na+ current exhibited both a tonic nature and use-dependence. (3) Tacrine at 100 μmol/L caused a negative shift (about 10 mV) in the voltage-dependence of steady-state inactivation of Na+ current, and retarded its recovery from inactivation, but did not affect its activation curve. (4) Intracellular application of tacrine significantly inhibited Na+ current. CONCLUSION: In addition to blocking other voltage-gated ion channels,tacrine blocked Na+ channels in guinea-pig ventricular myocytes. Tactine acted as inactivation stabilizer of Na+channels in cardiac tissues.