Iran is among the countries which change official time, every year according to their constitutions. Studies have shown an increase of incidence ratio (IR) of acute myocardial infarction by these time transitions. Despite annual time changes in Iran, there is no published data to prove this among the Iranian. This retrospective study examined the IR of patients with AMI, who were admitted to the Emergency Department (ED) of 5 teaching hospitals during the week just after the time transitions (observed period), with two weeks before and after the time transitions (expected period), both in spring and fall. In total, 11051 patients were admitted during the ten weeks (observed and expected), in both spring and fall time transitions. The IR of AMI during both observed and expected period did not show any significant difference (p > 0.05); however, the incidence of AMI was increased during the first week after the transition in spring (p > 0.05). Although the results of the present study did not prove the relation between time transitions and incidence of AMI, a slight increase existed for IR of AMI during three days after spring shift. This increase in IR of AMI can be due to Nowrooz, the national holidays which lasts four days after turning clocks forward in Iran.