Cranial blood flow, mean cranial transit time and cranial blood volume were measured by the intravenous RISA technique in 10 patients with cerebral transient ischemic attacks (TIA) at the various time intervals from the onset of last attack. Cranial blood flow was subnormal in 5 out of 11 determinations and mean transit time trended to be prolonged in the diseased hemisphere in cases suggestive of the unilateral hemispheric lesion. A decrease in cranial blood flow was observed in TIA with lowering of heart rate below 60/min, or with atrial fibrillation, whereas no obvious correlation was present between heart rate and cranial blood flow either in 94 patients with, or with 62 patients without cerebrovascular diseases. Cardiac dysrhythmias including bradycardia, leading to reduce perfusion to the brain was discussed as a possible factor for producing TIA.