OBJECTIVES: The time of onset of a myocardial infarction shows seasonal and daily variation. We aimed to investigate whether the number of hours with daylight has an effect on the seasonal variation of heart attack, and whether the time of sunrise has an effect on the diurnal rhythm of myocardial infarction. METHODS: We carried out a retrospective database study covering all patients admitted to any acute care hospital with the diagnose of myocardial infarction in Hungary in years 2004 and 2005 (n=32.329). Data was collected from the database of the National Health Insurance Fund Administration according to the International Classification of Diseases (ICD). Data on the time of sunrise and sunset was collected from the Hungarian National Meteorological Service. RESULTS: With consideration to seasonal variation, the peak period of a heart attack was found during the spring season, with lowest number of events during the months of summer. The number of hours with daylight showed a weak negative correlation with the occurrence of myocardial infarction (r= -0.108, p<0.05). With consideration to diurnal variation, the peak period of daily events was between 6-12 in the morning (35.57 %). We have found a positive correlation between the time of sunrise and sunset and the occurrence of myocardial infarction (p<0.01). CONCLUSIONS: Based on our findings, the number of hours with daylight and the time of sunrise may be connected with the chances of having a heart attack, however other factors may also have an influence.