The study included 42 patients with coronary heart disease operated on the coronary arteries. A potassium and magnesium asparaginate (PMA) solution, 450-1000 ml, was injected in 30 patients for 5-7 hours; other crystalloid solutions was used in a control group (n = 12). The concentrations of potassium and magnesium were measured prior to surgery, following initial anesthesia, before and after extracorporeal circulation (EC). The measurements suggested a significant potassium and magnesium intake at surgery under EC. The use of PMA solution showed its advantage in stabilizing the study electrolytes at the main surgical stages. Inclusion of PMA into infusion therapy considerably reduced a need for an additional use of concentrated KCl solution to maintain potassium at the preoperative level. Of particular importance was the use of PMA to maintain magnesium that was held in the upper normal range throughout the operation, as shown by both the median values and an individual analysis. When PLA was not administered, the mean concentration of magnesium was consistent with that in the lower normal electrolyte range and 50% patients developed hypomagnesemia. The comparative analysis of the clinical course after EC in both groups of patients with different levels of magnesium was indicative of the better status of some hemostatic parameters with the level of magnesium being maintained in the upper normal range.