We describe a three-year-old boy who presented with recurrent expectoration of bronchial casts six months following creation of a fenestrated lateral tunnel Fontan circulation for pulmonary atresia with intact ventricular septum. Cardiac catheterization demonstrated elevated central venous pressure with two areas of stenosis within the Fontan circuit, specifically at the junction of the right superior caval vein and the right pulmonary artery, and between the atrial baffle and the right superior caval vein. Insertion of Palmaz stents in these areas resulted in a reduction in central venous pressure, and a transient reduction in production of casts. Eight weeks after catheterization, however, he produced further casts, which resulted in hypoxia, respiratory arrest and death. We reviewed the autopsied specimens obtained from patients with the Fontan circulation over an eleven-year period at our institution in order to ascertain the prevalence of subclinical production of bronchial casts. We found no casts in the thirteen patients examined. Hemodynamic assessment is vital in all patients who develop this syndrome, and should be the primary focus of investigation, rather than solely directing efforts at lysis of casts.