The excess iron is stored in hemosiderin. This iron is in equilibrium, however, with a very small pool of so-called free iron in the cell. This pool of iron is so small that its size has never been satisfactorily determined. Better termed, loosely-bound iron, this material catalyzes the formation of reactive oxygen species through Fenton chemistry. These reactive oxygen species are the agents of cell injury.
Iron overload promotes the production of a number of reactive oxygen species.
Cardiac cells are particularly sensitive to oxidant-mediated injury since they must perform a number of complex functions which include contraction and transmission of electrical impulses. With iron loading, cardiac cells in culture begin to fail. Cardiac myocytes loose their characteristic pattern of beating under these culture conditions. Congestive cardiomyopathy is the most common cardiac defect that occurs with iron overload, but other problems have been described including pericarditis, restrictive cardiomyopathy, and angina without coronary artery disease. The integrated backscatter of the interventricular septum and posterior wall are higher than normal, perhaps due to iron deposition.