The antiphospholipid syndrome (APS) is defined by the presence of anti-phospholipid antibodies (aPLs) and venous or arterial thrombosis, recurrent pregnancy loss, or thrombocytopenia. The syndrome can be either primary or secondary to an underlying condition, most commonly systemic lupus erythematosus (SLE). Echocardiographic studies have disclosed heart valve abnormalities in about a third of patients with primary APS. SLE patients with aPLs have a higher prevalence of valvular involvement than those without these antibodies. Valvular lesions associated with aPLs occur as valve masses (nonbacterial vegetations) or thickening. These two morphological alterations can be combined and are thought to reflect the same pathological process. Both can be associated with valve dysfunction, although such association is much more common with the latter alteration. The predominant functional abnormality is regurgitation; stenosis is rare. The mitral valve is mainly affected, followed by the aortic valve. Valvular involvement usually does not cause clinical valvular disease. The presence of aPLs seems to further increase the risk for thromboembolic complications, mainly cerebrovascular, posed by valve lesions. Superadded bacterial endocarditis is rare but may be difficult to distinguish from pseudoinfective endocarditis. The current therapeutic guidelines are those for APS in general. Secondary antithrombotic prevention with long-term, high-intensity oral anticoagulation is advised. The efficacy of aspirin, either alone or in combination, is yet to be assessed. Corticosteroids are not beneficial and may even facilitate valve damage. Immunosuppressive agents should only be used for the treatment of an underlying condition. Current data suggest a role for aPLs in the pathogenesis of valvular lesions. aPLs may promote the formation of valve thrombi. These antibodies may also act by another mechanism, as indicated by the finding of subendothelial deposits of immunoglobulins, including anticardiolipin antibodies, and of colocalized complement components in deformed valves from patients with APS.