The aim of the study was to evaluate the usefulness of determining markers of myocardial damage, such as: aspartate aminotransferase, total creatine kinase, cardiac creatine kinase isoenzyme, total lactate dehydrogenase, cardiac lactate dehydrogenase isoenzyme and peripheral blood lactic acid in sport horses subjected to physical exertion. The research was carried out on 50 horses of three breeds: Ukrainian Riding, Hanoverian and Westphalian, aged 4-16 years. In all horses, the activity of: aspartate aminotransferase, total creatine kinase, cardiac creatine kinase isoenzyme, total lactate dehydrogenase, cardiac isoenzyme lactate dehydrogenase and lactic acid concentration were marked before and after exercise. It was found that after physical exercise in the tested horses, there was an increase in markers of myocardial damage. On the basis of the conducted research, it was demonstrated that the highest increase concerned the concentration of lactic acid and the activity of the cardiac isoenzyme of creatine kinase. The conducted studies additionally indicate that the evaluation markers of myocardial damage in horses may be useful as a screening test in detecting cardiac muscle disorders associated with excessive exercise. However, it should be emphasized that it must be considered together with the results of a clinical examination and additional tests such as cardiac ultrasound and electrocardiography.