We studied coexisting potential arterial and cardiac causes of stroke in 159 patients with nonvalvular atrial fibrillation (AF), who were admitted to a population-based primary care center for an anterior circulation infarct. Systematic investigations included brain CT, carotid Doppler ultrasounds with frequency analysis and echotomography, and mono- and bidimensional echocardiography. Lacunar infarction due to small-artery disease was at least as likely as an AF-related stroke in 13% of the patients who had hypertension and a small deep infarct. In 67% of the patients, internal carotid artery disease ipsilateral to infarct was present, but it was severe (greater than or equal to 50% stenosis or occlusion) in only 11%. There was a potential cardiac source of embolism other than AF in 14%. Overall, although only 18% of the patients had AF as the only potential cause of stroke, embolism from the heart remained the most likely etiology of infarct in 76%. Our findings emphasize the role of AF-related hemodynamic disturbances, which were often associated with embolic phenomena, and a rather low early risk of recurring embolism (4%) within the 1st month after stroke.