One of the quite frequent long-term effects of radiation therapy of malignant tumors, such as breast cancer and Hodgkin’s lymphoma primarily, when the irradiation of the mediastinum is performed, is the development of radiation-induced valvular disease. It is noted that the clinical manifestation of valve dysfunction can typically arise approximately 5 years after a course of anticancer radiotherapy. Thereafter in these patients increases the risk of infective endocarditis. However, in therapeutic and oncological clinical practice the difficulty of identifying and making the differential diagnosis of endocarditis in patients with “cancer” history is still quite common. At the moment cases of infective endocarditis after polychemotherapy and radiation therapy are not widely covered for cardiologists and internists in the medical literature. In addition before starting specific treatment due to the possible threat of infectious complications, including endocarditis, in oncology guidelines it is recommended to p