BACKGROUND Low cardiac output syndrome is defined as the need for a postoperative intra-aortic balloon pump or inotropic support for longer than 30 minutes in the intensive care unit. Mitral valve surgery is increasingly being performed in high-risk patients who might require mechanical circulatory support for low cardiac output syndrome. Therefore the aim of this study was to identify the preoperative predictors of low cardiac output syndrome after mitral valve surgery. METHODS We conducted a retrospective review of data prospectively entered into an institutional database. Between 1990 and February 2008, 3039 patients underwent isolated mitral valve surgery with or without coronary bypass surgery. The independent predictors of low cardiac output syndrome and operative mortality were determined by means of stepwise logistic regression analysis. RESULTS The overall prevalence of low cardiac output syndrome was 7%. The independent predictors of low cardiac output syndrome were urgency of the operation (odds ratio, 2.9), earlier year of operation (odds ratio, 2.4), left ventricular ejection fraction of less than 40% (odds ratio, 2.1), New York Heart Association class IV (odds ratio, 2), body surface area of 1.7 m(2) or less (odds ratio, 1.6), ischemic mitral valve pathology (odds ratio, 1.6), and cardiopulmonary bypass time (odds ratio, 1.02). The operative mortality was higher in patients with low cardiac output syndrome (30% vs 1.3%, P < .001). Overall operative mortality was 3.4%. The independent predictors of mortality were urgency of the operation (odds ratio, 7.1), renal failure (odds ratio, 4.3), nonuse of polytetrafluoroethylene sutures (Gore-Tex; W. L. Gore & Associates, Inc, Austin, Tex; odds ratio, 2.1), any reoperative surgical intervention (odds ratio, 1.8), increasing age (odds ratio, 1.03), and cardiopulmonary bypass time (odds ratio, 1.02). CONCLUSIONS Low cardiac output syndrome is associated with significantly increased morbidity and mortality. Novel strategies to preserve renal function, optimization of pre-existing heart failure symptoms, and use of artificial polytetrafluoroethylene sutures might reduce the incidence of low cardiac output syndrome and lead to improved results after mitral valve surgery.