In a study with 185 children with congenital heart disease undergoing surgical correction with the use of CPB, changes in serum levels of mannose binding lectin and activities of MBL‐MBL‐associated serine protease (MASP)‐1 and MBL‐MASP‐2 complexes were assessed immediately before, and during the surgery, throughout the first postoperative day and at discharge from the hospital. The gene discussed is MASP1; the disease is congenital heart disease.