To evaluate the differences between non-circular shape of FloWatch®-PAB and conventional pulmonary artery (PA) banding. Methods: Geometrical analysis. Conventional banding and FloWatch®-PAB perimeters were plotted against cross-sections. Computational fluid dynamics (CFD) model. CFD compared non-circular FloWatch®-PAB cross-sections with conventional banding regarding pressure gradients. Clinical data. Seven children, median age 2 months (7 days to 3 years), median weight 4.2 kg (3.2–9.8 kg), with complex congenital heart defects underwent PA banding with FloWatch®-PAB implantation. Results: Geometrical analysis. Conventional banding: progressive reduction of cross-sections was accompanied by progressive reduction of PA perimeters. FloWatch®-PAB: with equal reduction of cross-sections the PA perimeter remained constant. CFD model. Non-circular and circular banding provided same trans-banding pressure gradients for same cross-sections at any given flow. Clinical data. Mean PA internal diameter at banding was 13.3 ± 4.5 mm. After a mean interval of 5.9 ± 3.7 months, all children underwent intra-cardiac repair and simple FloWatch®-PAB removal without PA reconstruction. Mean PA internal diameter with FloWatch®-PAB removal increased from 3.0 ± 0.8 to 12.4 ± 4.5 mm (normal mean internal diameter for the age = 9.9 ± 1.6). No residual pressure gradient was recorded in correspondence of the site of the previous FloWatch®-PAB implantation in 6/7 patients, 10 mmHg peak and 5 mmHg mean gradient in 1/7. Conclusions: The non-circular shape of FloWatch®-PAB can replace conventional circular banding with the following advantages: (a) the pressure gradient will remain essentially the same as for conventional circular banding for any given cross-section, but with significantly smaller reduction of PA perimeter; and (b) PA reconstruction at the time of de-banding for intra-cardiac repair can be avoided.