Abstract: The calcium paradox model was made in cultured neonatal rat heart cells. The ⁴⁵Ca uptake by the cultured neonatal rat heart cells and the contents of sialic acid (SA) of the cultured heart cells were measured to observe and evaluate the protective effects of sodium paeonol sulfate against calcium paradox in the cultured heart cells. The resuits demonstrated that sodium paeonol sulfate 50～400μg/ml remarkedly inhibited the rapid (5 min)and the slow (12Omin)phases of 45/sup<>Ca uptake by the cultured heart cells and myocardial beating rate (MBR) under normal states. Besides inhibition of ⁴⁵Ca uptake by the cultured heart cells, this drug was found to elevate the contents of SA in the membrane of the cultured heart cells during calcium paradox. This indicates that the mechanism of protection against calcium paradox by sodium paeonol sulfate may be associated with blocking the slow calcium channel as well as increasing SA in the cell memberane.