Several diseases, particularly cardiovascular affections, show a periodic fluctuation in their occurrence. We studied the relation between the frequency of occurrence of myocardial infarction with the days of the week and the time of onset of acute myocardial infarction. Four hundred five patients with first AMI and within < 24 h of onset chest pain were enrolled in this study. The time of symptom onset was recorded and six hour periods were tested for a day. According to their gender and occupational condition all patients were divided into four categories. In conclusion; the frequency of acute myocardial infarction was not different between all groups according the days of the week. Also there was a relative high peak on Monday and Friday in working subjects but this was not statistically significant in the frequency of AMI in the days of the week when was compared with retired patients.