From a survey on 8,000 coronary angiographic studies performed in our Institute between January 1980 and June 1990, 105 patients were identified as having angiographically normal coronary arteries and myocardial infarction (MI). Coronary arteries considered as normal were subdivided in completely normal (Group I), or slightly abnormal, with minimal lesions resulting in less than 30% narrowing of a major artery, defined as mild coronarosclerosis (Group II). Thirty-five patients were excluded from the study, because of the lack of complete follow-up data; the remaining 70 patients represent the study group we examined. The following parameters were examined: sex, age at the time of acute MI, family of ischemic heart disease, hypertension, dyslipidemia, diabetes, smoking, stable or unstable angina before MI, location of the MI, ejection fraction (EF), presence of completely normal coronary arteries or mild coronarosclerosis. Follow-up was obtained by contacting the patients or their families; post infarction angina, reinfarction, sudden death or cardiac death were noted. The subjects were divided in 2 groups, according to the coronary anatomy; Group I consisted of 41 patients with completely normal coronary arteries and Group II consisted of 29 patients with mild coronarosclerosis. No significant statistical difference was noted between the 2 groups regarding age, sex and coronary risk factors (except for dyslipidemia which was significantly more prevalent in the subjects with mild coronarosclerosis). Prevalence of left ventricular impairment (EF < 45%) and coronary events (angina, reinfarction and death) were significantly higher in Group II. There was no significant difference in age or clinical risk factor prevalence between patients with complicated and non complicated clinical course.(ABSTRACT TRUNCATED AT 250 WORDS)