A 41-year-old man with atrial septal defect-Eisenmenger syndrome presented with progressively worsening breathlessness. The echocardiogram, computerized tomographic scan and magnetic resonance imaging of the thorax showed dilated pulmonary arteries and large thrombi in the right and left pulmonary arteries. Contrast-enhanced computerized tomographic scan was better than magnetic resonance imaging in picking up the thrombus. The possibility of in situ thrombus formation was considered more likely than thromboembolism, as there were none of the acute symptoms expected with the embolization of such large thrombi.