A previously healthy 2-year-old Guatemalan female with an undiagnosed chronic illness characterized by fever and rash had presented with anorexia, weight loss, periorbital edema, abdominal pain, and distention. A chest radiograph documented cardiomegaly. An echocardiogram demonstrated a pericardial effusion, dilated right atrium, right ventricle, and main pulmonary artery, as well as diminished right ventricular systolic function and pulmonary hypertension. Right ventricular systolic pressure was estimated at 90 mm Hg. Computed tomography of her chest was performed. There was no evidence of interstitial lung disease, but changes included dilated pulmonary arteries consistent with the presence of pulmonary hypertension as well as acute thrombosis of the superior vena cava and left brachiocephalic vein. These findings suggested thromboembolism as the etiology of pulmonary hypertension. A ventilation/perfusion lung scan also suggested differential lung perfusion. She was placed on systemic anticoagulation transiently. The presence of antiphospholipid antibodies (aPL) was documented as described below. Rheumatology consultation was requested for consideration of a possible autoimmune/inflammatory etiology.