Background: The article deals with the analysis of principal causes of valve prosthesis thrombosis and “pannus” thrombosis. The diagnosis and contemporary treatment strategy of prosthesis dysfunction have been considered. Material and methods: In our department 1670 patients with extracorporeal circulation were operated on, among them 1260 had valve pathology that made up 74.2%. 1164 heart valves were replaced, 145 of them were biological prostheses and 1019 were mechanical ones of different types. Prosthesis thrombosis took place in 28 patients that represented 60% of the number of patients with prothesis disfunction and 2.2% of the total number of operated patients from which 21 patients, their age ranged from 35 to 63 years old. The surgical treatment was performed to 9 patients, thrombolysis – to 19 patients. Results: During last 6-7 years the thrombolysis treatment with ateplasum and reteplasse has been successfully implemented in the therapy of thrombosis valve prothesis. Thrombolysis was performed to 19 patients. The results are the following: in 17 cases good outcomes (a complete recovery of the prosthesis function with transprosthetic gradient and the normalization of systolic pressure in right ventricle) have been registered, one case has been complicated with transitory ischemic ictus. Out of 19 patients who underwent the thrombolysis treatment, there were 2 lethal cases. Conclusions: The patients that are in a critical state with prosthesis thrombosis (acute pulmonary edema, hypotension, heart insufficiency NYHA IV) should immediately receive EchoCG confirmation of the need of intravenous thrombolitic therapy. The thrombolysis efficacy in prosthesis thrombosis is high; the rate of embolic complications is low, which can be used as the first line treatment for all patients with prothesis thrombosis (in the absence of contraindications). In the case of partial response to the thrombolysis treatment, the patient can be operated on in good hemodynamic conditions and with low surgical risk.