Interstitial cells of Cajal (ICC) generate the electrical slow wave. The ionic conductances that contribute to the slow wave appear to vary among species. In human, a tetrodotoxin-resistant Na⁺ current (NaV1.5) encoded by SCN5A contributes to the rising phase of the slow wave, while T-type Ca²⁺ currents have been reported from cultured mouse intestine ICC and also from canine colonic ICC. Mibefradil has a higher affinity for T-type over L-type Ca²⁺ channels and the drug has been used in the gastrointestinal tract to identify T-type currents. However, the selectivity of mibefradil for T-type Ca²⁺ channels over ICC and smooth muscle Na⁺ channels has not been clearly demonstrated. The aim of this study was to determine the effect of mibefradil on T-type, L-type Ca²⁺ and Na⁺ currents. Whole cell currents were recorded from HEK 293 cells coexpressing green fluorescent protein with either the rat brain T-type Ca²⁺ channel ₁3.3b + ₂, the human intestinal L-type Ca²⁺ channel subunits _1C + ₂, or Na_V1.5. Mibefradil significantly reduced expressed T-type Ca²⁺ current at concentrations 0.1 µM (IC₅₀ = 0.29 µM), L-type Ca²⁺ current at >1 µM (IC₅₀ = 2.7 µM), and Na⁺ current at 0.3 µM (IC₅₀ = 0.98 µM). In conclusion, mibefradil inhibits the human intestinal TTX-resistant Na⁺ channel at sub-micromolar concentrations. Caution must be used in the interpretation of the effects of mibefradil when several ion channel classes are co-expressed.