Objectives: To determine whether the biochemical marker cTnI with circulating value has forensic significance in the detection of myocardial damage in rats in experimental conditions of hyperthermia by exposure to water temperatures of 41 °C. Material and methods: The study was conducted on 24 adult Wistar rats that were divided into two experimental groups, depending on water temperature exposure of 37 °C (KG, n = 8) and 41 °C (G41, n = 16). Depending on the length of time of exposure to water temperatures of 41 °C are further divided into G41-AM (20 min of exposure), G41-PM (exposure until death). Blood for analysis of the concentration of cardiac troponin I (cTnI) was taken before the experiment and after the expiration of the given duration of the experiment of 20 min or death. The concentration of cTnI was determined in serum by ELISA method. The level of statistical significance was, p