Objective: To evaluate the feasibility of using atrial volume with three-dimensional echocardiography (3DE) in assessing pulmonary blood in children with tetralogy of Fallot (TOF). Methods: Twenty cases of TOF aged (3.2±4.7) years old were recruited, but plentiful shunts through atrial septum, severe valvular regurgitation and problems at atrial inlet or outlet were all excluded. Atrial volume was measured by 3DE and pulmonary blood was evaluated by angiography. Follow-up of atrial volume by 3DE was conducted within 1 week after surgical repair. Results: (1) According to McGoon index derived from angiography, the cases were divided into 2 groups. Compared with the the group with McGoon index > 1.5 (n=11), the volume of left atrium (LAV) was smaller in the group with McGoon index < 1.5 (n=9), [(20.2±2.1) ml/m2 vs. (16.7±1.2) ml/m2, t=4.414, p=0.000]. While, the volume of right atrium (RAV) was larger, [(23.5±2.2) ml/m2 vs. (27.7±1.3) ml/m2, t=5.120, p=0.000]. (2) After surgical repair, LAV was increased from (17.2±3.2) ml/m2 to (22.4±6.2) ml/m2, (t=3.941, p=0.001). However, no significant changes occurred with RAV, [(26.9±3.4) ml/m2 vs. (27.9±7.3) ml/m2, t=0.532, p=0.602]. The atrial volumetric ratio, defined as LAV / RAV, was increased from (0.8±0.2) to (1.0±0.3), (t=2.935, p=0.009). Conclusions: Atrial volume measured with 3DE is an index, which is able to reflect the pulmonary development in children with TOF. Smaller LAV and Larger RAV were observed in the group with less pulmonary blood supply. With the relief of obstruction after surgical repair, the increased LAV indicates the improved pulmonary blood supply.