ObjectiveTo study the catalytic activity of phospholipase A2and the concentrations of group I and group II phospholipases A2in the sera of patients during and after coronary artery bypass surgery.DesignProspective study.SettingUniversity hospital and research laboratory.PatientsFourteen consecutive patients operated on for ischemic heart disease.InterventionsThe catalytic activity of phospholipase A2and the serum concentrations of group I and group II phospholipases A2were measured before, during, and after the operation until the seventh postoperative day. A total of 196 blood samples were taken from 14 patients.Measurements and Main ResultsThe catalytic activity of phospholipase A2and the concentration of group II phospholipase A2increased in the sera of patients after coronary artery bypass surgery. The concentration of group I phospholipase A2did not change. The catalytic activity of phospholipase A2correlated significantly with group II but not with group I phospholipase A2values.ConclusionsThe increase in the catalytic activity of phospholipase A2in serum after coronary artery bypass surgery is due to group II phospholipase A2. The present results suggest that group II phospholipase A2is responsible for the physiologic and pathophysiologic effects of catalytically active phospholipase A2after coronary artery bypass surgery.(Crit Care Med 1996; 24:259-262)