The use of an obstructing balloon catheter positioned in the outflow tract of the pulmonary ventricle may be an alternative method for the adaptation of the left ventricle to an increased afterload prior to an arterial switch procedure in patients with complete transposition requiring a two-stage approach. We tested this approach in an acute hemodynamic study in a piglet model. Seven piglets were anesthetized with halothane and ventilated at FiO2 1.0. Through a median sternotomy, the great vessels were exposed. The right ventricular pressure and the aortic blood pressure were recorded using microtip manometers, cardiac output was measured by an electromagnetic flow probe on the ascending aorta. A 6F or 7F Berman angiographic catheter was placed in the lumen of the pulmonary artery and the balloon inflated to decrease cardiac output no more than 30%. The hemodynamic changes observed after balloon inflation included an 100% increase in systolic right ventricular pressure (control vs balloon inflation (mean±SE) 20.4 ± 1.5 mm Hg vs 46.6 ± 4 mm Hg, p<0.001), a slight reduction in systolic aortic pressure (75.5 ± 3.8 mm Hg vs 65.0 ± 5.8 mm Hg; p<0.05), and a reduction in cardiac output by 30% (1.1 ± 0.081/min vs 0.8 ±0.08 1/min, p<0.01). The systolic right ventricular to aortic pressure ratio was increased from 0.27 ± 0.02 to 0.69 ± 0.08, p<0.001. This study shows that a balloon catheter may be useful in creating systolic hypertension in the pulmonary ventricle in patients with complete transposition requiring a two-stage approach.