Venous thrombosis after pacemaker implant is a known, although often underrecognized condition that can challenge system revision or upgrading, leading occasionally to thromboembolic complications. Several factors are considered to promote thrombus formation. Among them, alteration of blood flow mechanics due to the presence of catheters in the vessel lumen may itself play a pivotal role. Hereby we present the case of a 65-year old men who underwent a dual-chamber pacemaker implant in another institute for sick sinus syndrome by means of left cephalic venous access. About two months later he started experiencing neck swelling, pain and dysphagia. Six months later, ultrasonography and CT-scan revealed complete jugular vein thrombosis caused by a lead loop at the level of the left subclavian vein. Of note, thrombosis occurred despite proper oral anticoagulation with warfarin undertaken for coexisting atrial fibrillation. It's important to keep in mind this possible complication of pacemaker implant to allow for early diagnosis and better treatment chances. This case report is an example of how proximal catheter displacement may promote thrombus formation, probably by affecting blood flow mechanics, even in spite of proper oral anticoagulation.