Cardiac c-kit(+) cells are generally believed to be the major population of stem/progenitor cells in the heart and can be used as a cell source for cardiomyoplasty; however, the cellular electrophysiological properties are not understood in this type of cells. The present study was designed to investigate functional ion channels in undifferentiated mouse cardiac c-kit(+) cells using approaches of whole cell patch voltage clamp, RT-PCR, and cell proliferation assay. It was found that three types of ionic currents were present in mouse cardiac c-kit(+) cells, including a delayed rectifier K(+) current (IK(DR)) inhibited by 4-aminopyridine (4-AP), an inward rectifier K(+) current (I(Kir)) decreased by Ba(2+), and a volume-sensitive chloride current (I(Cl.vol)) inhibited by 5-nitro-1-(3-phenylpropylamino) benzoic acid (NPPB). RT-PCR revealed that the corresponding ion channel genes, Kv1.1, Kv1.2, and Kv1.6 (for IK(DR)), Kir.1.1, Kir2.1, and Kir2.2 (likely responsible for I(Kir)), and Clcn3 (for I(Cl.vol)), were significant in mouse cardiac c-kit(+) cells. The inhibition of I(Cl.vol) with NPPB and niflumic acid, but not IK(DR) with 4-AP and tetraethylammonium, reduced cell proliferation and accumulated the cell progression at G(0)/G(1) phase in mouse cardiac c-kit(+) cells. Our results demonstrate that three types of functional ion channel currents (i.e., IK(DR), I(Kir), and I(Cl.vol)) are present in mouse cardiac c-kit(+) cells, and I(Cl.vol) participates in regulating cell proliferation.