Magnetic resonance imaging--the evaluation of choice in residual shunt after congenital heart disease surgery? Accurate anatomic diagnosis presents a dilemma in patients with residual shunt after corrective surgery for congenital heart disease. We describe a patient who, after atrial septal defect repair, developed dyspnea and central cyanosis despite normal pulmonary arterial pressures and right heart chamber size. A role for early MRI is suggested. 