All patients with systemic lupus erythematosus in a prospective, epidemiologically based study within a defined area in southern Sweden were invited to participate in an investigation of cardiac function. From 1981 to 1988, 101 patients were included in the study, and 75 of them were investigated according to a fixed protocol by echocardiography, Doppler cardiography, electrocardiography (ECG) at rest and at exercise, and myocardial scintigraphy (in patients whose ECG became abnormal during exercise). IgG anticardiolipin antibodies (IgG aCL) were determined by ELISA. Twenty of the 75 patients (27%) had valvular disease and 12 of these (60%) had increased concentrations of IgG aCL, compared with 12 of 55 (22%) without valvular disease (p less than 0.01). Pericardial effusion was detected in 14 patients (19%) during the study period. Mild pulmonary hypertension was found in 11 patients (16%), who also had increased frequency of IgG aCL. Myocardial infarction had occurred in 7 patients, 3 of whom were women less than 40 years of age. Echocardiography revealed regional hypokinesis or akinesis in 5 of the patients with myocardial infarction. Exercise testing revealed low work capacity in 13 of 54 patients (24%), the limiting symptoms being mainly exhaustion or musculoskeletal pain. An abnormal resting ECG was found in 9 of the patients participating in the exercise test. During exercise, abnormal ST-depression was observed in 8 patients, 2 of whom developed angina. Myocardial scintigraphy was performed in 6 of these patients, revealing reversible uptake defects in all. Prolonged glucocorticoid treatment was associated with valvular abnormalities as well as myocardial infarction. Valvular abnormalities and IgG aCL appeared to be risk factors for cerebral infarction.