Adriamycin (ADR) causes morphological and functional alterations in mitochondrial structure in the heart. The study's aim was to determine whether there is a protective effect of selenium (Se) on ADR-induced cardiac damage. Rats were divided into four groups: The first group was injected saline intraperitoneally (i.p.) for 21 days; the second group received 4 mg/kg i.p. ADR every alternate day for 8 days; the third group received 50 mu g/kg i.p. Se for 21 days; and the fourth received the Se (for 21 days) and ADR (for 8 days) coadministration i.p. Left ventricular functions, electrocardiography parameters, and blood pressures were assessed. Mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) level, and thioredoxin reductase (TrxR) activity were determined. Total antioxidant (TAS) and oxidant status (TOS) in cytosol, mitochondria of myocytes, and plasma were measured. Left ventricular data demonstrated left ventricular systolic pressure (LVSP) decreased, left ventricular developed pressure (LVDP) decreased, and left ventricular end-diastolic pressure (LVEDP) increased in ADR-treated animals, compared to the control and Se groups. ADR decreased the membrane potential and ATP level in myocyte mitochondria. TrxR activity decreased in the ADR group, compared to the Se group. Cytosolic and mitochondrial TAS decreased and mitochondrial and plasma TOS increased in the ADR group, compared to the control. The coadministration of Se with ADR attenuated left ventricular dysfunction, improved MMP and ATP levels, and prevented oxidative stress by increasing antioxidants (especially TrxR) and decreasing oxidants. We concluded that Se is effective against ADR-induced cardiac damage via the restoration of TAS and TOS, which prevented mitochondrial damage.