The present study deals with the effect of calcium entry blocking agent, nitrendipine, on the rat heart sarcolemmal (Na,K)-ATPase. Nitrendipine (1 mumol/l) exerted a stimulatory effect on (Na,K)-ATPase activity. Kinetic analysis of enzyme activation by increasing concentrations of sodium in the presence of nitrendipine revealed a 67% increase in Vmax value and a decrease of the apparent Ka value to 33% of that in control. The observed influence on (Na,K)-ATPase may contribute indirectly to the calcium antagonistic effect of nitrendipine.