Purpose: to evaluate the features of the course of complications in patients with BAV based on the results of a pathomorphological study.Material and methods: a retrospective analysis of a register of 328 patients with AS and dilation of the ascending aorta (DAA), based on histological studies performed in 2010–2022 was carried out. 209 patients were diagnosed with BAV as a result of histological examination, and 119 patients were diagnosed with tricuspid aortic valve (TAV). The type of BAV was analyzed in 139 operated patients based on the results of the analysis of surgical protocols.Results: according to the obtained results, the first type with fusion of the right and left coronary cusps prevailed among patients with BAV (78%), the smallest number of patients with BAV was with fusion of the right coronary and non-coronary cusps of the aortic valve (4%), while fusion of the left coronary with the non-coronary cusps of the aortic valve (AV) and patients with "true" BAV occurred in each case in 9% of patients. The formation of AS (75.6%), DAA (68.4%), and the combination of AS+DAA (81%) was more observed in the group of patients with the first type of BAV. According to the results of histology of the AV, there were no significant differences depending on the morphology of the valve. In particular, according to the results of AV histology, the frequency of calcification did not differ in groups of patients with BAV and TAV. Fibrosis with erasing of the layered histoarchitectonics of the AV of varying severity was detected in every second patient, regardless of the presence of congenital heart disease (CHD). According to the results of aortic histology, hemodynamic aneurysm in patients with BAV was much more common than in patients with TAV (p=0.0027). In addition, it was verified that in 39 patients out of 40 without pathomorphological changes in the aortic wall, aortic stenosis appeared in the diagnosis, of which 80% of patients had CHD: BAV. It was verified that 39 out of 40 patients without pathomorphological changes in the aortic wall had aortic stenosis in the diagnosis. Moreover, in 80% of patients, the main cause of aortic dilatation was identified as BAV.Conclusions: the results of this study demonstrated that in the vast majority of cases, aortic dilatation and aortic stenosis are formed during fusion of the right and left coronary cusps. The absence of morphological changes in the aortic wall in almost every third patient with DAA and BAV, confirms the genetic contribution to the formation of aortic dilatation in this category of patients and requires further study.