An arteriovenous fistula (AVF) is an abnormal direct communication between an artery and a vein, bypassing the capillary bed. AVFs may be acquired (post-traumatic, post-procedural) or surgically created for hemodialysis access. On color Doppler, an AVF produces a perivascular tissue vibration artifact (color bruit) around the communication site. Spectral Doppler of the feeding artery shows high-velocity, low-resistance flow; the draining vein shows arterialized pulsatile flow. Hemodialysis fistula surveillance is a core component of vascular technology practice.