BACKGROUND We aimed to evaluate the impact of membranous interventricular septum (MIS) length and calcifications of the native aortic valve (AV), via preoperative multidetector computed tomography (MDCT) scan, on postoperative atrioventricular block III (AVB/AVB III) and permanent pacemaker implantation in surgical aortic valve replacement (SAVR). METHODS We retrospectively analyzed preoperative contrast-enhanced MDCT scans and procedural outcomes of patients affected by AV stenosis who underwent SAVR at our center (June 2016-December 2019). The study population was divided into two groups (AVB and non-AVB), and variables were compared with a Mann-Whitney's U-test or chi-square test. Data were further analyzed using point biserial correlation and logistic regression. RESULTS A total of 155 (38% female) patients (mean age of 71.2 ± 6 years) were enrolled in our study: conventional stented bioprosthesis (N = 99) and sutureless prosthesis (N = 56) were implanted. A postoperative AVB III was observed in 11 patients (7.1%). AVB patients had significant greater calcifications in left coronary cusp (LCC) -AV (non-AVB = 181.0 mm3 [82.7-316.9] vs. AVB = 424.8 mm3 [115.9-563.2], p = 0.044), LCC left ventricular outflow tract (LVOT) (non-AVB = 2.1 mm3 [0-20.1] vs. AVB = 26.0 mm3 [0.1-138.0], p = 0.048), right coronary cusp (RCC) -LVOT (non-AVB = 0 mm3 [0-3.5] vs. AVB = 2.8 mm3 [0-29.0], p = 0.039), and consequently in total LVOT (non-AVB = 2.1 mm3 [0-20.1] vs. AVB = 26.0 mm3 [0.1-138.0], p = 0.02), while their MIS was significantly shorter than in non-AVB patients (non-AVB = 11.3 mm [9.9-13.4] vs. AVB = 9.44 mm [6.98-10.5]; p=0.014)). Partially, these group differences correlated positively (LCC -AV, r = 0.201, p = 0.012; RCC -LVOT, r = 0.283, p ≤ 0.001) or negatively (MIS length, r = -0.202, p = 0.008) with new-onset AVB III. CONCLUSIONS We recommend including an MDCT in preoperative diagnostic testing for all patients undergoing surgical AVR for further risk stratification.