Infectious endocarditis (IE) is a contagious polyposis ulcerative inflammation of the endocardium, accompanied by lesions of the heart valve apparatus and endothelium by various pathogenic and opportunistic pathogens. Mainly mitral and aortic valves are affected, less often - tricuspid valve. The purpose of this study was to report two cases of IE in cats. Due to the low prevalence of the disease in cats, there is no clear diagnostic algorithm, so the diagnostic search is complicated. In both cases, autonomic lesions of the heart valve apparatus were observed. In the first clinical case, we could hardly diagnose the disease because of its rapid progression: initial echocardiogram result was normal, but after 48 hours, the cat's condition became much worse, and 18 hours later, it died. In the second case, histopathological examination confirmed an infectious inflammatory process of the endocardium and myocardium of unclear genesis. However, the presence of lower respiratory tract infection and the absence of additional laboratory tests, such as bacterial blood culture and PCR diagnosis, limited us in proposing a hypothesis about the origin and etiology of IE.