Aim To evaluate the effect of the total time of myocardial ischemia on results of the treatment of patients with ST segment elevation acute myocardial infarction (STEMI) who underwent percutaneous coronary interventions (PCI).Material and methods This study used data from a hospital register for PCI in STEMI from 2006 through 2017. 1649 patients were included. Group 1 consisted of 604 (36.6 %) patients with a total time of myocardial ischemia not exceeding 1880 min; group 2 included 531 (32.2 %) patients with a duration of myocardial ischemia from 180 to 360 min; and group 3 included 514 (31.2 %) patients with a duration of myocardial ischemia longer than 360 min.Results Mortality was lower in group 1 (2.3 %) than in groups 2 and 3 (6.2 and 7.2 %, respectively; p1-2=0.001; p1-3<0.001; p2-3=0.520). The incidence of major cardiac complications ("adverse cardiac events", MACE) was lower in group 1 (4.1 %) than in groups 2 and 3 (7.3 and 9.5 %, respectively, p1-2=0.020; p1-3<0.001; p2-3=0.200). The incidence of no-reflow phenomenon was higher in group 3 (9.7 %) than in groups 2 and 3 (4.5 and 5.3 %, respectively (p1-2=0.539; p1-3=0.001; p2-3=0.005). The major factors associated with the increased total time of myocardial ischemia >180 min were age (odd ratio, OR, 1.01 at 95 % confidence interval, CI, 1.0 to 1.02; р=0.044), female gender (OR, 1.64 at 95 % CI 1.26 to 2.13; р<0.001), chronic kidney disease (OR 1.82 at 95 % CI 1.21 to 2.74; р=0.004). Performing prehospital thrombolysis was associated with a decrease in the total time of myocardial ischemia (OR 0.4 at 95 % CI 0.31 to 0.51; р<0.001). A strong direct correlation was observed between the total time of myocardial ischemia and the time from the onset of pain syndrome to hospitalization (r=0.759; р<0.001).Conclusion The total time of myocardial ischemia >180 min was associated with increased mortality and development of MACE. The total time of myocardial ischemia > 360 min was associated with increased incidence of the no-reflow phenomenon. The major predictors for the time of myocardial ischemia >180 min included age, female gender, and chronic kidney disease. The use of pharmacoinvasive strategy was associated with an increased number of patients with a total duration of myocardial ischemia <180 min. The contribution of the time of prehospital delay to the total time of myocardial ischemia was greater than the contribution of the "door-to-balloon" time. The time of prehospital delay showed a strong direct correlation with the total time of myocardial ischemia.