Prevention of venous thrombosis after cardiac devices implantation is an important health issue to be considered by cardiac pacing experts. This prevention is justified by the high incidence of these obstructions causing major clinical and technical complications during device upgrade, lead replacement procedures, other diagnostic or therapeutic interventions that require venous catheterization. However, the usefulness of prophylactic therapeutic strategies to prevent these complications remains unknown. This books reports the results of the first randomized clinical trial designed to assess the effects of warfarin in the prevention of these complications in high-risk patients. After cardiac device implantation, 101 patients were randomly assigned to Warfarin (target INR= 2.0–3.5), or to Placebo. Clinical and laboratory evaluations were performed regularly up to 6 months post-implant. Venous lesions were detected at 6 months by Digital Subtraction Venography. The analysis of our results allowed us to conclude that oral anticoagulation with warfarin had a beneficial preventive effect against the development of transvenous lead-associated thrombosis in high-risk patients.