What’s That Sound on a Vein Ultrasound? When we scan your leg veins with ultrasound, we actually listen to the blood flow too! Here’s what we hear: Normal Veins: We hear a smooth, soft “whoosh” when blood flows toward the heart. It sounds calm and steady, sometimes with little pulses as you breathe or when we squeeze your leg. Refluxing (Leaky) Veins: We hear an extra “backward whoosh” — like a gurgle or echo — after we squeeze your leg or have you bear down (like during a Valsalva). That sound