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Most recently, the possible impact of transitions to and from daylight saving time (DST) on the increased incidence of acute myocardial infarction (AMI) has been suggested. The goal of this report was to analyze independent influence of DST transitions on the incidence of AMI with simultaneous control for the confounding presence of situational triggers such as physical exertion, emotional stress, heavy meals, and sexual intercourse, as well as for other clinical factors. Detailed information was obtained from 2412 patients and included baseline characteristics, working status, exact time of AMI, possible external triggers, cardiovascular risk factors, and prehospital medication. AMI incidence on days after the DST was compared with incidence during control periods and patient characteristics, cardiovascular medication, and circumstances of AMI were evaluated to identify potential risk modifiers. Relative risks of AMI and differences in patient characteristics were expressed through incidence ratios and odds ratios, respectively, with 95% confidence intervals (CIs). Multivariate analysis was performed by using a stepwise multiple regression to assess the independent predictive significance of the characteristics of patients for the AMI occurring in the posttransitional period. The incidence ratio for AMI for the first four workdays after the spring DST transition was 1.29 (95% CI: 1.09-1.49) and the excess was particularly prominent on Monday. In autumn, the incidence ratio for AMI for this 4-d period was 1.44 (95% CI: 1.19-1.69), with peaks on Tuesday and Thursday. The independent predictors for AMI during this period in spring were male sex (p = 0.03) and nonengagement in physical activity (p = 0.02) and there was a trend for the lower risk of incident among those taking calcium antagonists (p = 0.07). In autumn, the predictors were female sex (p = 0.04), current employment (p = 0.006), not taking β-blocker (p = 0.03), and nonengagement in physical activity (p = 0.02). The present report supports the possibility that DST transitions represent additional chronobiological feature of AMI, and that risk of an onset varies according to sex, employment status, and the taking of cardiovascular medication.