ObjectiveTo investigate the risk or protective factors for systemic embolism (SE) in patients undergoing bioprosthetic mitral valve replacement (MVR). Methods Between October 2002 and March 2013, a total of 146 patients underwent bioprosthetic MVR. There were 78 females and 68 males with mean age of 66.23±5.17 years. The primary reason of mitral valve disease was mitral valve degeneration or mitral valve leaflet prolapse in 40 patients, rheumatic heart valve disease in 101 patients, ischemic heart disease in 3 patients, infectious endocarditis in 1 patient, and mechanical peri-valvular leak in 1 patient. All patients were given anticoagulation therapy with warfarin for 3 months. Thereafter, antithrombotic medication was prescribed according to the surgeon's preference. The patients were followed up by telephone or mail for postoperative condition and SE events. ResultsSixteen (10.96%) patients developed SE events, including cerebral infarction in 13 cases, transient ischemic attack (TIA) in 2 cases and spleen infarction in 1 case. A total of 16 patients died during follow-up. The 1-year, 3-year, 5-year and 10-year cumulative survival rate after surgery was 95.2%, 93.6%, 92.5% and 88.3% respectively. Patients with SE events had lower rate of left atrial appendage obliteration than those without SE events (25.0% vs. 78.6%, P=0.015). Multivariate analysis showed that left atrial appendage obliteration was an independent protective factor for SE in patients undergoing bioprosthetic MVR (P=0.041). ConclusionLeft atrial appendage obliteration is a major protective factor for systemic embolism in patients undergoing bioprosthetic MVR no matter what antithrombotic medication is taken.