Three-hundred and nine patients, 242 males and 67 females diagnosed of myocardial infarction were studied during the acute phase and followed for a year to evaluate any differences. The corrected incidence was greater amongst males, 11.1 vs 3.6/10,000 inhabitants. The presenting age was significantly lower in males below 50 and greater in women above 70. Hypertension, hypercholesterolemia and sedentariness were more prevalent amongst women; smoking was more prevalent amongst males. Infarction presentation was typical in both sexes being significant a 5 hour delay in arriving to the hospital in female patients. On hospital admission Killip III-IV was significantly more frequent amongst women (17% vs 4.6%). Hospital mortality although it was higher in women this was not statistically significant (19.4% vs 14.4%). During follow up there was a better control of risk factors in the male patients. Heart failure and mortality were greater amongst women during the first three months (p less than 0.001). Mortality differences continued being statistically significant during the following three months. From the sixth month to the first year, mortality rates were similar. The study suggests that infarction prognosis is worse in females.