This report describes one the first cases of antiphospholipid syndrome and Libman-Sacks endocarditis in a bioprosthetic valve. A redo mitral valve replacement was carried out owing to early deterioration of the prior valve. Initially it was considered secondary to rheumatic heart disease; however, pathology analysis and autoimmune workup revealed antiphospholipid syndrome with Libman-Sacks endocarditis. We believe certain populations with mitral valve stenosis may have an underlying antiphospholipid syndrome. As a result, there needs to be a lower threshold for identifying this disease. (C) 2016 by The Society of Thoracic Surgeons