Abstract: The negative inotropic effect of Pra-C was supposed to be related to the blocking of extracellular calcium influx but direct evidence is not known. We, therefore, examined the effects of PraC on Ca²⁺ i in isolated rat ventricular myocytes using the fluorescent Ca²⁺- indicator Fura-2/AM. It was found that Pra-C inhibited the elevation of Ca²⁺i induced by potassiumdepolarization, high extracellular calcium and calcium agonist Bay K 8644 in a dose-dependent manner. At 1.0 μmol · L^-1, it decreased the Ca²⁺i at the presence of 75 mmol · L^-1 KCl, 10 mol · L^-1 CaCl and 3 μmol · L^-1 Bay K 8644 by 50, 31 and 42% respectively. No significant effect on ouabain evoked Ca²⁺i increase was found, showing that it does not affect sarcolemmal Na⁺ —Ca²⁺exchange. These results further indicate that Pra-C may decrease the Ca²⁺i of myocyte by blocking voltage-dependent calcium channels.