Objective: The authors hypothesized that average precardiopulmonary bypass (pre-CPB) transesophageal echocardiographic (TEE) mean gradient (PG m ) and aortic valve area (AVA) values would be significantly different from preoperative transthoracic (TTE) values in the same patients and that these changes would affect pre-CPB TEE grading of aortic stenosis (AS).Design: Retrospective, observational design. Setting: Single university hospital. Participants: The study comprised 92 patients who underwent aortic valve replacement with or without coronary artery bypass grafting between 2000 and 2012 at Duke University Hospital and who had PG m and AVA values recorded in both pre-CPB TEE and preoperative TTE reporting databases.Interventions: None. Measurements and Main Results: PG m with pre-CPB TEE was lower by 6.6 mmHg (95% confidence interval, -4.0 to -9.3 mmHg; p o 0.001), whereas AVA was higher by 0.10 cm 2 (95% confidence interval, 0.04 to 0.15 cm 2 ; p o 0.001), compared with preoperative TTE values. When using PG m , pre-CPB TEE generated an AS severity 1 grade lower 39.1% of the time and revealed no difference 55.4% of the time compared to preoperative TTE. When using AVA by continuity, pre-CPB TEE generated an AS severity 1 grade lower 14.1% of the time and revealed no difference 81.5% of the time compared to preoperative TTE. When using either PGm or AVA, preoperative TTE exhibited moderate or severe AS for all study patients, whereas, pre-CPB TEE demonstrated mild AS in 5.4% (n ¼ 92) of patients.Conclusions: The authors confirmed their hypothesis that pre-CPB TEE generates different PG m and AVA values compared with preoperative TTE. These differences often underestimate AS severity. Hemodynamic standardizations or adjustments of pre-CPB TEE PG m and AVA values may be necessary in anesthetized patients before assigning an AS grade using these parameters. & 2016 Elsevier Inc. All rights reserved.KEY WORDS: aortic stenosis, aortic valve area, discordance, mean gradient, precardiopulmonary bypass (intraoperative) transesophageal echocardiography P RECARDIOPULMONARY BYPASS (pre-CPB) transesophageal echocardiography (TEE) is essential for intraoperative assessment and surgical guidance during cardiac surgery. Although many patients come to the operating room with an extensive cardiac workup, pre-CPB TEE aortic valve assessment can affect surgical decision-making based on new findings during planned or emergency surgeries. According to a large retrospective review of 3,835 patients undergoing isolated coronary artery bypass grafting (CABG), 3.3% of patients had an unplanned aortic or mitral valve procedure added to the surgery based on pre-CPB TEE findings. 1 Of 1,823 patients undergoing mitral valve surgery, 1.0% of patients underwent an unplanned aortic valve procedure based on incidental findings during pre-CPB TEE. 1 Given that surgical decisions can be based on pre-CPB TEE findings, accurate interpretation of grading parameters during the pre-CPB period is imperative.The validated mean gradient (PG m ) and aor...