To more accurately predict the optimal pulmonary artery (PA) reconstruction procedure (Lecompte manoeuvre or original Jatene procedure) during the arterial switch operation (ASO), we focused on the horizontal sectioning (HS) angle between the left hilum PA and the great arteries using preoperative computed tomography (CT) imaging. We defined the HS angle α (β) as the angle between the tangential line from the posterior (anterior) wall of the left PA at the hilum to the left anterior (right posterior) surface of the main PA and the tangential line from the left surface of the ascending aorta to the left anterior (right posterior) surface of the main PA. We identified 14 consecutive patients diagnosed with transposition of the great arteries (TGA) or TGA-type double-outlet right ventricle who underwent preoperative CT imaging. The original Jatene or Lecompte procedure was used for nine (OJ group) and five (L group) patients. Relationships of the great arteries of the OJ and L groups were side-by-side in eight and two patients, oblique in one and one patient, and anteroposterior in zero and two patients, respectively. In the OJ group, β was greater than α in all patients. The median α/β value was 0.618. In group L, α was greater than β in all patients. The median α/β was 1.307. Left PA stenosis caused by stretching was not observed in the L group. Coronary obstruction was not identified in the OJ group. Left PA stenosis behind the neo-ascending aorta was observed in one patient in the OJ group and required reoperation. The HS angle may be a useful predictor of optimal intraoperative PA reconstruction during ASO, especially for side-by-side or oblique relationships.