The lack of significant cardiac dysfunction in our Hamp−/− mice and in other reported mouse models of impaired hepcidin production (29–31) is in contrast with the clinical characteristics of juvenile hemochromatosis, in which patients develop severe cardiomyopathy (5). This contrast points to possible differences between human and murine cardiomyocytes in iron entry, export, storage, or detoxification pathways. In the context of iron overload, the entry of NTBI into cardiomyocytes is recognized as a contributor to cardiac iron loading and subsequent dysfunction (18–20). Therefore, interesting questions are whether known NTBI transporters differ in human and mouse cardiomyocytes and whether such differences account for the divergent cardiac phenotypes.