A venous duplex scan is a painless examination of the veins that return the blood back to the heart. The procedure uses ultrasound to view the inside of the veins. The two types of scans are an upper extremity venous duplex scan which assesses the veins in neck, shoulders, arms, and wrists. In a lower extremity venous duplex scan, the legs and ankles are viewed. A clear jelly is placed on the area and a probe is used lightly over the skin to take images of the veins. These images are then projected onto the screen. You may be asked to take deep breaths, holding them for a few seconds. This is called a Valsalva maneuver.