['Few data support an association between blood pressure variability and clinical outcomes during cardiac surgery. We tested the hypothesis that intraoperative systolic blood pressure variability outside a targeted blood pressure range predicts 30-day mortality in patients undergoing cardiac surgery.', 'Electronically captured blood pressure data from 7,504 consecutive coronary bypass surgery procedures between September 1, 1996, and December 31, 2005, were divided into development and validation cohorts. Systolic blood pressure variability episodes outside a blood pressure range (e.g., higher than 135 or lower than 95 mmHg) were characterized by number of episodes, magnitude of episode, duration of episode, and magnitude x duration of excursion (i.e., area under the curve). Multiple logistic regression analysis was used to assess 30-day mortality association. The most predictive mortality risk characteristic and blood pressure range was tested in the validation cohort.', 'A total of 3.1 million intraoperative blood pressure evaluations were analyzed. Systolic blood pressure variability was derived in 5,038 patients and validated in 2,466 patients (8% without cardiopulmonary bypass and 6% with valve procedure). Among all tested indices of blood pressure variability, mean duration of systolic excursion (outside a range of 105-130 mmHg) was most predictive of 30-day mortality (odds ratio = 1.03 per minute, 95% CI 1.02-1.39, P < 0.0001).'] Does intraoperative systolic blood pressure variability predict 30-day mortality in aortocoronary bypass surgery patients?