Intracardiac thrombi have rarely been reported in patients with the antiphospholipid syndrome. We describe a new case revealed by systematic echocardiography in an asymptomatic woman who consulted for mild thrombocytopenia. Our case is characterized by a past history of migraine, fetal loss and psychiatric disturbances and by a high level of antiphospholipid antibodies (anticardiolipin, anti-β<sub>2</sub>-glycoprotein I and lupus anticoagulant). Echography, in the absence of any cardiovascular symptom, showed bulky right intra-atrial thrombi requiring surgical excision. Histopathological analysis revealed the fibrino-cruoric nature of the lesion without myxoma. This case shows that, when faced with a mild thrombocytopenia associated with antiphospholipid antibodies, echocardiography may reveal a life-threatening and completely asymptomatic intracardiac thrombosis.