Background <p>We aimed to establish the most predictive echocardiographic indicator of appropriate tightness of bilateral pulmonary artery banding (BPAB).</p> Methods <p>In part A of the study, we retrospectively analyzed the peak flow velocity (PV) and nadir flow velocity (NV) across the band and the ratio of NV to PV (velocity ratio: VR) to determine appropriate band tightness. In part B, we prospectively studied the utility of the best predictive indicators.</p> Results <p>Thirty-one patients undergoing BPAB were enrolled in part A and identified as having appropriate pulmonary blood flow (APF), high pulmonary blood flow (HPF), or low pulmonary blood flow (LPF) during the postoperative period. The areas under the receiver operating characteristic curve (AUC) for HPF were 0.92 for PV, 0.99 for NV, and 0.99 for VR; the velocity thresholds were 2.47, 1.15, and 0.45&#xa0;m/sec, respectively. For LPF, the AUCs were 0.63 for PV, 0.78 for NV, and 0.81 for VR, and the velocity thresholds were 2.70, 1.59, and 0.58&#xa0;m/sec, respectively; thus, VR best indicated band tightness. In part B, we performed BPAB in 34 patients, adjusting the bands to achieve VRs between 0.45 and 0.58. The prevalence of HPF was significantly lower in part B than in part A, whereas those of LPF did not differ.</p> Conclusion <p>In BPAB, we consider the optimal range of VR at banding site is between 0.45 and 0.58.</p>