Pre- and postoperative left ventricular (LV) function was assessed by Doppler echocardiography in 95 infants who underwent open heart surgery during the past two and half years. The patients were divided into three groups: 43 patients with ventricular septal defect (VSD group), 37 with atrial septal defect (ASD group) and 15 with the tetralogy of Fallot (TOF group). Echocardiography was performed before and at an early stage after surgery (average: 11.6 days) in all cases. The forward flow velocity pattern was evaluated by Doppler echocardiography, placing the sample volume at the pulmonary vein (PV) and the LV inflow portion. At the PV, the peak velocity of the S wave during systole (p-PV_S) and the D wave during diastole (p-PV_D) in patients with ASD were significantly lower (p<0.01) postoperatively. In patients with VSD, only p-PV_D was significantly lower (p<0.05) postoperatively, showing a decrease of pulmonary blood flow. These results are thought to reflect a difference in the compliance of the left atrium between the two groups. At the LV inflow portion, the ratio of peak velocity of the wave during atrial systole to R wave on rapid inflow during diastole (A/R) was significantly lower in patients with VSD (p <0.01) postoperatively. At the same time, LV ejection fraction and fractional shortening were significantly lower (p<0.01), but these values remained within the normal range. These results suggest that LV can maintain a sufficient systolic performance against the decrease in preload and the increase in afterload as well as the improvement of diastolic function during the early period after surgery in the VSD group. In patients with ASD or TOF, there were no significant differences in parameters of LV function between preoperative and postoperative periods.