The prevalence of chronic atrial fibrillation (AF) and the clinical features in 151 patients with transient ischemic attacks (TIA) and in 349 patients with cerebral infarct have been analyzed. AF was found in 11.9% of patients with TIA and in 14.9% of patients with cerebral infarct. The difference was not significant (NS). In patients without AF, the carotid artery TIAs represent 70.6% of all TIAs, while the vertebral basilar artery TIAs account for 29.4%. When AF is present, 88.9% of all TIAs belong to the carotid artery and 11.1% to the vertebral basilar artery circulatory system (NS). TIAs lasting less than 10 minutes are 42.1% when AF is not present, while when AF is present they are only 11.1% (p less than 0.001). In patients without AF 79% of TIAs last less than one hour, while in patients with AF the percentage goes down to 38.9% (p less than 0.001). In patients with or without AF, the chronic digitalis therapy before the hospitalization does not affect in any way the occurrence of TIA or cerebral infarct. These results suggest that emboli from the atrium are more likely to cause cerebral infarcts than TIAs and when they cause TIAs more usually they last hours than minutes.