Objective — to identify risk factors and optimal preventive methods for intraoperative immediate hypersensitivity in cardiac patients. Material and methods. The study included 3878 cardiac patients. A retrospective analysis enrolled 2780 patients (group 1), prospective analysis — 1098 patients (group 2). Mean age was 60±11.2 years. Allergic anamnesis of patients, epidemiology and clinical structure of immediate hypersensitivity reactions were analyzed. Patients were divided into 3 subgroups depending on allergic history. Prevention of intraoperative hypersensitivity reactions was different in both groups. Diagnosis of hypersensitivity reactions to drugs was made on the basis of clinical symptoms in accordance with immediate hypersensitivity reaction severity scale. Laboratory examination was additionally applied in group 2 (histamine and serum tryptase levels). Results. Immediate hypersensitivity reactions occurred in 53 (1.37%) of cases. Incidence of this event was higher in group 1 (1.69%, n=47) compared with group 2 (0.55%, n=6, p=0.009). Anaphylactic shock occurred in 4 (0.11%) patients of the 1st group. Patients with sensitization to several substances or combination of any type of allergy with allergic diseases are more likely to experience intraoperative immediate hypersensitivity reactions than other patients (p<0.05). In these patients, incidence of hypersensitivity reactions was 5.71% of group 1. Reactions were not observed in group 2 (p=0.048). Hypersensitivity reactions were more common in 41 (1.73%) patients (p=0.0139) undergoing on-pump cardiac surgery. Histamine level was significantly higher within 40 min after immediate hypersensitivity reaction onset than in patients without this complication (p=0.0171). Protamine (32%) and antibiotics (20.7%) were the most common causes of intraoperative immediate hypersensitivity reactions (p<0.05). The cause of hypersensitivity reaction was unclear in 9% of cases considering simultaneous administration of several drugs. Conclusion. Risk factors of immediate hypersensitivity reactions in cardiac patients are previous allergic reactions and on-pump surgery. Identification of high risk patients and the use of comprehensive prevention protocol are effective for prevention of intraoperative hypersensitivity reactions.