Considering the prevalence of cardiovascular pathology and the increase in coronary interventions, including coronary artery bypass grafting (CABG), therapeutic observation and assessment of results, as well as possible complications in this cohort of patients is an urgent problem in the clinic of internal medicine. Autovenous conduits, namely the great saphenous vein, is one of the most common conduits during coronary artery bypass grafting. The reported incidence of minor dilation of great saphenous vein grafts used for CABG varies up to 14 %, but significant dilation of the aneurysm is rare. When performing coronary angiography or multispiral computed angiography, it is possible to establish the true size of the aneurysm, but the presence of mural thrombi can distort the true picture. Complications may include compression of the native coronary vessels, distal embolization, myocardial ischemia, compression of the right atrium, or fistula formation and rupture into the right atrium. The article discusses a rare clinical case of aneurysmal dilatation of an autovenous conduit up to 7.3 cm after 23 years of coronary artery bypass grafting. Considering that the development of aneurysms and pseudoaneurysms in the field of coronary bypass surgery can occur both early and late, clinical vigilance is necessary throughout the entire period of follow-up and informing the patient. The article discusses diagnostic and treatment algorithms for identifying aneurysms and pseudoaneurysms.