Elevation of cell iron content was produced by use of a lipophilic iron ligand, 8-hydroxyquinoline (HQ), capable of transferring catalytically active iron into cells. The Fe 3 + -HQ complex labeled with 5 9 Fe was avidly taken up by isolated perfused hearts contrary to the hydrophilic complex Fe 3 + -citrate. Hearts perfused in aerobic conditions with Krebs-Henseleit buffer were exposed for 15 min to the iron complexes, Fe 3 + -HQ (5μm/10μmand 10μm/20μm), or Fe 3 + -citrate (10μm), and then perfused for 30 min with normal buffer. Exposure to the high dose of Fe 3 + -HQ (10μm/20μm) resulted in early and irreversible decreases in coronary flow and heart rate (-48% and -33%, respectively), initial increases followed by decreases in left ventricular systolic pressure and +dP/dt, and increase in left ventricular end-diastolic pressure (+80%). The low dose of Fe 3 + -HQ (5μm/10μm) mimicked with a lower magnitude the effects of the high dose, whereas Fe 3 + -citrate had no effects on cardiac parameters. Only hearts exposed to the high dose of Fe 3 + -HQ exhibited a significant increase (+60%) in thiobarbituric acid-reactive substance level, an index of lipid peroxidation. The production of hydroxyl radicals was investigated by measuring 2,3-dihydroxybenzoic acid level in the coronary effluent after addition of salicylic acid (1 mm) in the perfusate. An immediate and high increase (x6) was seen during heart exposure to Fe 3 + -HQ (10μm/20μm) and to Fe 3 + -citrate (10μm). Considering Fe 3 + -citrate had no effect on cardiac function and lipid peroxidation it was concluded that this hydroxyl radical formation occurring in the extracellular space was not implicated in Fe 3 + -HQ-induced cardiac dysfunction. These results demonstrate the deleterious effect of increasing intracellular reactive iron level in non-ischemic hearts.