This prospective study describes valvular abnormalities assessed by transesophageal echocardiography (TEE) in patients with primary antiphospholipid syndrome (APLS) over a 5-year follow-up. Of the 56 patients with APLS evaluated at baseline, 47 (84%) had repeat TEE examinations, including 3 patients who died before the end of the follow-up. The first TEE study showed cardiac involvement (thickening or vegetations and embolic sources) in 34 subjects (61%), with mitral valve thickening, the most common abnormality, present in 30 patients (54%). Embolic sources were found in 14 patients (25%; 9 severe spontaneous echocardiographic contrast, 5 Libman-Sacks endocarditis), associated with mitral valve thickening or stenosis in 10 patients. Over the 5-year follow-up, cardiac involvement was unchanged in 30 subjects (64%). New cardiac abnormalities were observed in 17 patients (36%), 15 (88%) with high immunoglobulin-G (IgG) anticardiolipin antibody (aCL) titers and 2 (12%) with low IgG aCL titers. In conclusion, this study showed that mitral valve thickening and embolic sources are frequently observed in patients with APLS. Anticoagulant and/or antiplatelet treatment was ineffective in terms of valvular lesion regression. New appearances of cardiac involvement are significantly related to high IgG aCL titers.