The purpose of the study. To study the possibility of using the domestic preparation cytoflavin to prevent the transition of the preclinical stage of cardiomyopathy overvoltage to the clinical stage. Material and methods. The study included 45 sportsmen, in whom the examination revealed an increase in myocardial antigen in the blood against the background of lack of clinical and electrocardiographic signs of cardiomyopathy overvoltage. The athletes were divided into 2 groups: 23 sportsmen of the main group took cytoflavin, 22 sportsmen of the control group did not receive the preparation. The level of myocardial antigen was determined in the reactions of passive hemagglutination and inhibition of passive hemagglutination by reducing the antimicrocardial test serum titre. To control the severity of oxidative stress oxLDL in serum was determined by immunoenzyme assay. All athletes were conducted electrocardiography, Holter 24-hour monitoring, echocardiography. Results. In sportsmen of the main group after the course of treatment with cytoflavin a decrease in oxidative stress severity by oxLDL level was established, in sportsmen of the control group oxidative stress severity on the background of decrease in general physical efficiency increased. The examination after 1 month showed that cardiomyopathy overvoltage according to electrocardiography and Holter monitoring data occurred in 16 athletes of the control group and only in 1 athlete of the main group. The efficacy of cytoflavin to prevent the transition of preclinical stage of cardiomyopathy overvoltage to clinical stage was 93.75%. Conclusion. The efficacy of cytoflavin application in sportsmen at the preclinical stage of cardiomyopathy overvoltage is conditioned by its ability to reduce the oxidative stress severity as one of the links in the pathogenesis of cardiomyopathy overvoltage, which significantly reduces the probability of transition of the preclinical stage of the pathology to the clinical stage. It is advisable to use cytoflavin in sports medicine to prevent the transition of preclinical stage of cardiomyopathy overvoltage to clinical stage.