In the past years, cardiovascular progenitor cells have been isolated from the human heart and characterized. These cells can differentiate into cardiomyocytes, smooth muscle cells and endothelial cells and are therefore of great value for investigation of the mechanisms that drive progenitor cell function and plasticity, drug testing and, potentially, therapeutical purposes. In this respect, most studies have focused on enhancing differentiation with chemicals or growth factors, or co-culture with other cell types. Although they have revealed important mechanisms, protocols need to be established that exclude the need for such factors when one considers using progenitor cells to repair the human heart. In this study we tested whether we could induce cardiomyogenic differentiation of human cardiomyocyte progenitor cells (CMPCs) by altering their membrane potential. We induced hyperpolarization in CMPCs by either co-culturing them with a K(ir)2.1-overexpressing cell line or by overnight culture in medium containing low potassium concentrations. Hyperpolarization led to increased intracellular calcium concentrations, activation of calcineurin signaling, increased cardiac-specific gene and protein expression levels and, ultimately, to the formation of spontaneously beating cardiomyocytes. Thus, hyperpolarization is sufficient to induce differentiation of CMPCs, thereby revealing a novel mechanism for cardiomyogenic differentiation of heart-derived progenitor cells.