A narrow and calcified sinotubular junction (STJ) represents a risk for ascending aortic dissection after balloon-expandable transcatheter aortic valve implantation (TAVI). The aim of this study was to assess computed tomography (CT)-based aortic root morphology in patients with aortic stenosis (AS), and to evaluate the feasibility of a two-step inflation technique that we devised for TAVI using the SAPIEN 3 in patients with a narrow and calcified STJ. We retrospectively analyzed the STJ diameter (STJD) as well the as aortic annulus diameter (AAD) and STJ calcification using CT imaging in 412 patients undergoing TAVI. We defined a "narrow STJ" as a minimum STJD that was smaller than the diameter corresponding to a 10% oversized annulus area, and a "calcified STJ" as an STJ calcification angle > 90°. A "narrow and calcified STJ" was identified in 54 patients (13.1%) of patients. Among them, we performed TAVI using the two-step inflation technique with SAPIEN 3 in 20 patients and compared with 11 patients that underwent the conventional inflation procedure. Two-step inflation was successfully performed without ascending aortic dissection in all 20 patients. The effective orifice area index at discharge in these 20 patients was similar to that in 11 patients who underwent the conventional inflation procedure for a "narrow and calcified STJ" [1.40 (1.20-1.51) vs. 1.33 (1.18-1.41) cm/m, p = 0.23]. Although further assessment is required, the two-step inflation technique with the SAPIEN 3 is feasible for a narrow and calcified STJ.