Lithium salts are used in treating many neurotic and psychosomatic disorders. Studying the toxic effects of this medication is necessary because doctors commonly keep their patients on long-term lithium treatment. The goal of the current study was to assess the cardiotoxic effect of lithium on adult Wistar albino rats and the possible role of oxidative stress and the protective effect of selenium. Twenty-four adult male Wistar albino rats were divided into four equal groups; control, selenium-treated group; received 0.2 mg/kg/d dissolved in distilled water, lithium-treated group; received 53 mg/kg/day of lithium carbonate dissolved in 1 ml 0.9% sodium chloride orally by gavage, and lithium-and-selenium treated group received lithium and selenium in the previous doses. After 90 days, we demonstrated that rats received lithium (53 mg/kg/day) demonstrated a significantly higher malondialdehyde (MDA) level and a significantly lower glutathione (GSH) level compared to controls indicating induction of oxidative stress in the cardiac tissues. In addition, there was a marked rise in cardiac biomarker cardiac troponin I (cTnI) level. The immunohistochemistry examination of the heart for caspase3 expression revealed a significant increase in the lithium group in comparison with the control. These results suggest that lithium-induced cardiotoxicity in rats is due to oxidative stress& apoptosis. Selenium administration significantly mitigated lithium's cardiotoxic effects. It can be used to alleviate the cardiotoxic effects of lithium.