The new protocols of actuation in acute myocardial infarction thrombolysis have increased the number of patients treated, and have changed their characteristics. To assess the influence that this event has had in the complications incidence and mortality rate, we revise 704 infarcts treated with thrombolytic in a coronary unit, during 8 years. We separate two groups: 1) Patients treated since november 1983 to december 1988 following the established protocol at the beginning of this therapeutic (n = 328). 2) Patients treated since this date to july 1991, with a new protocol that include older than 70 years patients, moore than 6 hours of therapeutics delay and use of another thrombolytics, moreover streptokinase (n = 376). These changes have increased the number of thrombolysis in the second group (24.6 vs 49.1%; p < 0.001). Nevertheless being a higher group of risk we have found neither a significant mortality increase (6.40 vs 7.71%; p = NS), nor complications related to the thrombolysis: The incidence of major hemorrhages were 2.13 vs 1.06% (p = NS), cerebral hemorrhages 0.91 vs 1.6% (p = NS), hypotension related to the thrombolytics 15.55 vs 5.85% (p < 0.001). Neither has had significant difference in the incidence of reinfarcts (6.42 vs 5%; p = NS). In conclusion, the great number of thrombolysis realized nowadays, due to the actuation protocols changes, have increased significantly, neither the complications related with this therapeutic, nor the mortality rate, nor the reinfarcts number.