Many statistics demonstrate a definite improvement of myocardial infarction during hospitalization, especially a decrease in the mortality. It appears tempting to credit that improvement to the numerous modifications of the treatment of this dangerous disease in the last few decades. The study reported here indicates, however, that other factors must be taken into account. We compared the evolution of two groups of patients hospitalized for acute myocardial infection, 10 years apart: The first group (G1) of 731 patients corresponds to years 1970-1975; the second group (G2) of 729 patients, corresponds to the years 1984-85-86. During these ten years, mortality decreased by 38 p. cent, from 19.2 p. cent (G1) to 11.9 p. cent (G2). This decrease remains significant regardless of age and sex, except in two subgroups with the least number of patients, i.e. women under the age of 65 and men over 65. It should be noted that rhythm disorders occur with the same frequency in both sub-groups while atrio-ventricular blocks seem to have decreased. The difference in the mortality cannot be attributed to the patient's selection. In fact, in both groups, they are comparable regarding the men/women ratio, the age distribution and the presence of main risk factors (tobacco abuse, dyslipidemia, arterial hypertension, diabetes, heredity). The treatment results in many alterations especially concerning diuretics which seem to be used in approximately 30 p. cent of the patients in both groups. On the contrary, steroids, prescribed in 25.3 p. cent of G1 patients are abandoned; electro-systolic stimulation established in 21.2 p. cent of G1 patients, concerned only 4 p. cent of G2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)