Carotid artery stenting is an alternative to carotid endarterectomy for patients at high risk for surgery for carotid artery stenosis. Although unfractionated heparin is routinely used, there are no published data evaluating the optimal activated clotting time during carotid stenting. In a retrospective analysis of 605 patients who underwent carotid stenting using unfractionated heparin at the Cleveland Clinic Foundation, the optimal peak procedural activated clotting time associated with the lowest combined incidence of death, stroke, or myocardial infarction was 250 to 299 seconds.