Intracellular calcium distribution was studied in myocardial cells of mice by using pyroantimonate cytochemistry and EDX microanalysis. The results demonstrated that both OPP and PPP methods had a selective localization of intracellular bound calcium, and OPP method was more sensitive to calcium. The distribution of calcium in myocardial cells is highly departmentalized, and its mam pools were confined to sarcoplasmic reticulum and mitochondria. Calcium eylochemical localization is very useful in studying the effect of calcium in metabolism and pathogenesis of myocandial cells.