There have been few reports documenting the outcome of arterial swich operations(ASO) in selected patients with transposition of great arteries(TGA) and with left ventricular outflow tract obstruction(LVOTO). In the case of TGA with LVOTO, if the atrial septal defect(ASD) is large and the ventricular septal defect(VSD) is restricive, this deprives the left ventricle(LV) of approporiate preload and could lead to underdevelopment of the ventircular mass and lead poor LV performance after the arterial switch operation, dspite a high pressure in the LV preoperatively. Because an increase in the systolic ventricular pressure is not necessarily paralleled by an increase in ventricular mass, which is also essential for optimal ventricular performance after the operation. We report here a case of rapid LV training after ASO in TGA with unprepared LV (because of large ASD and restrictive VSD) despite a high pressure in the LV(due to LVOTO) preoperatively.