Background: Horizontal aorta (HA) is an anatomical feature that can pose significant technical challenges for the successful positioning of the bioprosthetic valve during transcatheter aortic valve replacement (TAVR). Physiological range of aortic angle (AA) is unknown; hence there is no cutoff AA for classifying HA. Moreover, patient characteristics predicting HA are under-investigated. Methods: This was a retrospective analysis of prospective collected data from 16 heart valve centers in Europe. The study utilized a common dataset with a priori agreed-upon definitions and variables. Eligible patients underwent TAVR between 2014 and 2020 and had multidetector computed tomographic imaging data available for determining the AA. The analysis described the distribution of AA and potential predictors of HA. Inter-center variability was also explored. Results: For 4022 patients analyzed, the mean AA ± standard deviation was 49.4° ± 9.4° (median 49°, inter-quartile range [IQR] 12°, range 18–90°). There was no significant difference in mean AA between men and women (49.4° ± 9.1° vs. 49.6° ± 9.3°, respectively; p = 0.53); therefore, 49.4° was accepted as the cutoff value for HA in subsequent analyses. Covariates significantly associated with HA included age (odds ratio [OR]: 1.02, 95% confidence interval [CI]: 1.01–1.04, p < 0.001), body mass index (OR: 1.06, 95% CI: 1.05–1.08, p < 0.01), previous cardiac surgery (OR: 0.58, 95% CI: 0.45–0.75, p < 0.001), and porcelain aorta (OR: 0.66, 95% CI: 0.52–0.85, p = 0.001). Some inter-center variability was observed. Conclusions: We defined 49.4° as the mean AA, and also associated predictors of HA in a large case series of patients with severe aortic stenosis candidates for TAVR.