Abstract: The protective effects of tetrandrine (Tet) on calcium paradox in isolated Langendorffs heart in rats were investigated. Tet was shown to reduce the release of lactate dehydrogenase (LDH) and protein from myocardial tissues and the loss of K⁺, Mg²⁺ and accumulation of Ca²⁺, Na⁺ in myocardial tissues during calcium paradox in a concentration—dependent manner. Decrease of Fe and Zn and increase of Cu in myocardial tissues were observed in calcium Paradox and Tet 27 μmol/L was found to inhibit the decrease of Fe and Zn. In addition, Tet was also found to inhibit the decrease of Ca²⁺ and the increase of Na~+ in myocardial tissues during calcium—free perfusion. These results indicate that Tet can protect the myocardium against calcium paradox by stabilizing cellular membrane and inhibiting the influx of Ca²⁺.