We describe a 5-year-old boy with Fontan physiology and a ventricular pacemaker who developed severe plastic bronchitis. Evaluation by cardiac catheterization revealed profoundly altered hemodynamics, which improved with atrial pacing. Following implantation of an atrial pacemaker, which restored atrioventricular (A-V) synchrony, the patient's hemodynamics greatly improved and his plastic bronchitis resolved.