EDN1 and atherosclerosis: Resting coronary microvascular resistance tend to be higher compared with hyperemia which is objectively displayed with invasive hemodynamic measurements by Fineschi et al.10 Endothelin-1 levels, a strong vasoconstrictor mediator, have been demonstrated to be elevated in CSF patients reflecting increased vasomotor tonus.11 Impaired endothelial function looks like another pathophysiological mechanism responsible for coronary slow flow as it has been in atherosclerosis.