Abstract: The present invention discloses an inhibitive effect of Na+—K+-ATPase caused by a compound selected from the group consisting of magnesium lithospermate B (MLB), isomer, prodrug, derivative, pharmaceutically acceptable salt, and a composition thereof. In this invention, the variations of Na+—K+-ATPase activity were monitored with increasing MLB concentrations, and the result shows the Na+—K+ ATPase activity is repressed by MLB. An outcome of the inhibitory effect, the function of cellular sodium/potassium exchanger is reduced and cellular calcium ion concentration is increased. The cerebral ischemia test exhibited MLB provides an effective repression of cell infarct. That is, the MLB is useful for inhibiting the function of cellular Na+—K+ pump, and further brings the utility for cardiac stimulation, diuretic enhancement, heart failure curing, anti-anoxia, neurocyte apoptosis protection, apoplexy prevention and treatment, and so on.