We studied the cardiotoxicity in magnesium (Mg)-deficient male rats fed 50μg/g Cd for 45 consecutive days. Cd at a low con-centration (0.28ppm) in the heart induced cardiotoxic effects manifested by a decrease of the heart rate and weight and histopathological changes in the presence of Mg deficiency though Cd supplementation to a normal diet did not induce any cardiotoxic effect. Cardiac output (CO) did not increase in response to the decrease in the total peripheral resistance (TPR) in the Mg-deficient rats fed Cd, suggesting that supplementation of Cd to the Mg-deficient diet may lead to a decrease in the myocardial contractile function. However, supplementation of Cd to Mg-deficient diet also alleviated myocardial necrosis and Ca overload observed in the heart of Mg-deficient rats. The present data suggest that Cd ameliorates Ca overload in the heart of Mg-deficient rats but also may inhibit the release of Ca²⁺, which is a major determinant of the level of contractile force.