Background A third to half of the patients with primary antiphospholipid syndrome have valve disease. Methods and Results The echocardiographic characteristics of primary antiphospholipid syndrome were analyzed, and the utility of treatment with anticoagulants and/or antiplatelet agents (acetylsalicylic acid) is examined with the use of transesophageal echocardiography in the evaluation of valvular lesions after 1 year of therapy. Twenty-nine patients, 22 women and 7 men with average age of 35.4 years, were studied. Transesophageal echocardiography was performed on all patients before beginning anticoagulant and/or antiplatelet treatment. Valve lesions were found in 22 (75.9%) patients. Of these, other cardiac abnormalities were found in 3 cases, myocardial infarction in 2, and atrial septal defect in 1. In 7 (24.1%) cases, no valvular abnormality was detected, although in 1 of these, alterations in left ventricular segmental wall movement secondary to myocardial infarction were found. One year after initiation of anticoagulant and/or antiplatelet therapy, it was possible to perform transesophageal echocardiograms on 13 patients. No modification of valve lesions was found in 6 (46.2%) cases; new lesions had appeared in the remaining 7 (53.8%) as well as left ventricular apical akinesis in 1 case. Conclusions These results indicate that the predominant heart lesion in primary antiphospholipid syndrome is valvular; anticoagulant and/or antiplatelet treatment does not diminish the noninfective valve lesions, and on occasion this entity may be associated with myocardial infarction despite angiographically normal coronary arteries. (Am Heart J 1999;137:974-9.)