CECs and HUVECs express eNOS. (A) High-power (650×) light photomicrograph of an endothelial nitric oxide synthase–positive circulating endothelial cell from a patient with a recent acute myocardial infarction. Confirmation that the cell is endothelial is depicted by strong binding to CD146 coated magnetic beads (4μm in diameter). (B) “Positive control” photomicrograph (160×) of a cluster of 3 endothelial nitric oxide synthase–stained human umbilical vein endothelial cells. Note that staining is limited to the cytoplasm where most nitric oxide synthase is located. Images were visualized using an Axiostar Plus microscope (Zeiss, Welwyn Garden City, UK); objective lens, 40× and 10×; eyepiece, 10×. Images were captured using a Camedia C3030 camera, and transfered to JPG using standard smart card technology.