Figure 5a. Eisenmenger syndrome in a 36-year-old woman. Axial ECG-gated spin-echo images show atrial septal defect (arrow in a) and marked enlargement of the main pulmonary artery (PA) (b), consistent with pulmonary arterial hypertension. Long-standing severe pulmonary arterial hypertension can result in the shunt reversal that characterizes Eisenmenger syndrome. Ao = ascending aorta, LA = left atrium, RA = right atrium.