The content of total blood plasma protein and its fractions in absolute quantities was studied in patients with acquired and congenital heart lesions in different terms of the early postoperative period (82 patients) after operative procedures, performed under conditions of artificial blood circulation. The indices were compared in two groups of patients showing different regimens of protein loss replenishment and normalization of the protein metabolism during the operation and after it. There were observed considerable intraoperative losses of protein that remained also during 3-4 days following the operative procedure. Therefore, some recommendations are given as to the substitutive protein therapy.