A seasonal variation with an incidence peak during the colder period of the year, as well as a circadian distribution with a single peak of stroke onset in the morning hours are described in various countries. Cardioembolic stroke seems to be the most frequent stroke subtype among Greek patients. Atrial fibrillation is identified as the most frequent cause of stroke. Analysis of the temporal pattern of symptom onset in a series of over 300 Greek patients with first-ever cardioembolic acute stroke due to atrial fibrillation revealed a circannual distribution with a peak during winter and a decline of stroke occurrence during summer. Analysis of the diurnal variation of symptom onset in this stroke subgroup showed a distribution with 2 incidence peaks between 08:00-10:00 and 16:00-18:00. A relation between the second, however lower, frequency peak and the traditional Greek habit of afternoon sleep (siesta) could be assumed. Possible clustering of cardiologic events in patients with atrial fibrillation, especially during the time interval after awakening from night and afternoon sleep, could be a plausible explanation, which certainly deserves to be further investigated.