In contrast to Fpn fl/fl Myh6.Cre+ mice, patients with ferroportin disease, an inherited disorder of iron metabolism caused by dominant loss of FPN function, have not been reported to have cardiac complications (27, 28). However, although Fpn fl/fl Myh6.Cre+ mice retain intact FPN function in the duodenum, liver, and reticuloendothelial system, patients with ferroportin disease do not, leading to iron accumulation in the spleen and liver, reduced circulating Tf and NTBI, and marginal anemia (28). Given the known role of NTBI in cardiac iron overload, it is plausible that decreased NTBI entry into cardiomyocytes in these patients offsets the iron-loading effects of loss of cardiac FPN. This hypothesis is supported by our finding that dietary iron restriction protects Fpn fl/fl Myh6.Cre+ mice from developing cardiac dysfunction.