Magnesium orotate dihydrate (MO) has the sum formula C10H6MgN4O8 x 2H2O and a MG of 370.52. The salt is poorly soluble in water and hence does not bind gastric acid nor does it exhibit noteworthy laxative effects upon oral administration in contrast to easily dissociable Mg salts. As a source of magnesium (Mg), MO is indicated for the oral treatment of extracellular Mg deficiency. Orotic acid (OA), the second active ingredient of MO, is a key intermediate in the biosynthetic pathway of pyrimidines and is shown to improve the energy status of injured myocardium by stimulating, a.o., the synthesis of glycogen and ATP. Myocardial energy-rich phosphate levels are decreased during hypoxic conditions; subsequently, intracellular Mg is depleted and lost via the urine. Since binding sites for Mg (ATP) are provided by OA it can be classified as "Mg-fixing agent". Accordingly MO is also indicated for the treatment of Mg depletion as convincingly shown in animal experiments and also in coronary heart patients undergoing e.g. aortocoronary bypass surgery.