A man in his 50s with dilated nonischemic cardiomyopathy and reduced ejection fraction was referred for implantation of an implantable cardioverter defibrillator. After preparation of the left cephalic vein and failure to place the lead, a puncture of the left subclavian vein was attempted but was unsuccessful. Implantation was discontinued, and venography of the left subclavian vein was performed the next day. The venography showed thrombosis of the left subclavian vein, with a network of small veins (Figure, Video). Further history revealed that the patient was a manual worker who engaged in repetitive arm motion. The diagnosis of primary effort thrombosis subclavian vein, or Paget-Schroetter syndrome, was confirmed. Paget-Schroetter syndrome is a rare condition and refers to primary thrombosis of the subclavian vein at the costoclavicular junction.1 This rare finding serves as reminder that there are patients with Paget-Schroetter syndrome who have no symptoms as a result of developing fine networks of venous collaterals.