AbstractThe aim of this investigation was to examine the role of perforin (P)‐mediated cytotoxicity in the dynamics of tissue damage in patients with non‐ST‐segment elevation myocardial infarction (NSTEMI) treated with anti‐ischaemic drugs. We enrolled 48 patients with NSTEMI in this study [age, 71.5 years; 61.5/76 (median, 25th/75th percentiles)]. The percentage of total peripheral blood P+ lymphocytes was elevated owing to the increased frequency of P+ cells within natural killer (NK) subsets, T and NKT cells in patients on day 1 after NSTEMI when compared with healthy controls. Positive correlations were found between cardiac troponin I plasma concentrations and the frequency of P+ cells, P+ T cells, P+ NK cells and their CD56+dim and CD56+bright subsets during the first week after the NSTEMI. The expression of P in NK cells was accompanied by P‐mediated cytotoxicity against K‐562 targets at all days examined, except day 21, when an anti‐perforin monoclonal antibody did not completely abolish the killing. The percentage of P+ T cells, P+ NKT cells and P+ NK subsets was the highest on the day 1 after NSTEMI and decreased in the post‐infarction period. CD56+ lymphocytes were found in damaged myocardium, suggesting their tissue recruitment. In conclusion, patients with NSTEMI have a strong and prolonged P‐mediated systemic inflammatory reaction, which may sustain autoaggressive reactions towards myocardial tissue during the development of myocardial infarction.