ABSTRACT: Persistent alteration to host polymorphonuclear cell (PMN) physiology has been demonstrated after cardiac surgery performed with cardiopulmonary bypass (CPB). However, to date, PMN physiology and function beyond the first 24 h have not been investigated after cardiac surgery performed without CPB (off-pump coronary artery bypass grafting [OPCAB]). Blood samples of 15 patients were collected preoperatively and on days 1, 3, and 5 after OPCAB. Expression of CD11b, CD18, CBRM1/5, and CD62L were assessed by flow cytometry under resting conditions and after stimulation with formyl methionyl-leucyl-phenylalanine (fMLF), and respiratory burst activity was also measured. Under resting conditions, PMN CD11b, CBRM1/5, and CD62L expressions were minimally altered by surgery. Compared with the response of preoperative PMNs, PMNs assayed on days 3 and 5 after OPCAB demonstrated a significantly blunted increase in the expression of CD11b and CBRM1/5 after fMLF, significantly diminished shedding of CD62L in response to platelet-activating factor and fMLF, and diminished superoxide production after stimulation on day 3. The alteration of PMN function after OPCAB implies that cardiac surgical trauma without CPB directly modulates host PMN physiology.