Abstract: AimTo study the effects of hydrocortisone sodium succinate on sodium current in human atrial myocytes and in guinea pig ventricular myocytes. MethodsSingle cardiac myocytes were isolated by enzyme. The effects of hydrocortisone sodium succinate on sodium current (iNa) were assessed by applying whole-cell patch clamp techniques. ResultsHydrocortisone sodium succinate (1, 3, 10 μmol·L_-1) was shown to inhibit iNa of both human atrial myocytes and guinea pig ventricular myocytes in concentration dependent manner and the IC₅₀ were 6.97 and 8.74 μmol·L_-1, respectively. The inhibition effects acted quickly (1-3 min) and the maximal activating voltage of iNa was not changed in both human and guinea pig cardiac myocytes. Conclusion Hydrocortisone sodium succinate can exhibit inhibitory effects on iNa in both human and guinea pig cardiac myocytes, and its inhibitory effects act rapidly, which are not consistent with genomic effects, so there may be nongenomic effects.