Data on the 2,008 patients in the Swedish Co-operative Study from 1969 were compared with 773 consecutive cases with definite myocardial infarction (MI) admitted to the coronary care unit (CCU) of Danderyd Hospital in Stockholm 1984-85. We found a significant decrease in hospital mortality from 26.6% to 12.9% despite the admission of older patients to our CCU. Mean age for men was 63.8 vs. 65.6 years and for women, 69.8 vs. 72.3. The incidence of previous hypertension and diabetes was higher and the incidence of heart failure and angina lower in 1984-85. No differences were noted as regards the incidence of ventricular fibrillation, atrial fibrillation and AV-block III in the acute phase despite a much more frequent use of antiarrhythmics in 1969 (33% vs. 4%). A decreased use of cardiac glucosides was also noted (34% vs. 16%). Asystole, however, was noted in 10% of the patients in 1969 compared with 3% in our patients. beta-Adrenergic blockers were not used in 1969 but commonly given in 1984-85 (67%), also in those with heart failure (54%). Delay between onset of symptoms and admission was longer in 1969, 47% being admitted within 6 hours compared with 75% in 1984-85. In conclusion, our study shows a marked change in the use of various cardiac drugs in the treatment of MI. Differences between the populations as regards mortality and different clinical findings are more difficult to evaluate and may also be explained by change in the selection of patients treated in the CCU.