The efficiency of magnesium ascorbate, a new Romanian cardioprotector drug, was studied in guinea pigs and Wistar rats, both normal and with scurvy, within the framework of morphophysiological investigations of the pathogenesis of myocardial disease induced by large doses of beta-adrenergic substances of the isoproterenol type. The preventively treated animals presented only disseminated myocardial ultrastructural lesions within reversible limits. Biochemically, as compared with controls, a return to normal levels of ATP and Mg2+ and a decrease in the uptake of 45CaCl2 by the myocardium were observed. The pharmacological mechanisms of action of magnesium ascorbate are discussed.