 There are growing numbers of endocardial permanent pacemakers PPM and implantable cardioverter defibrillators ICD and cardiac resynchronization therapy CRT device. Asymptomatic obstruction of the access vein reported to have a high incidence 30-50 in some studies. This complication can cause some difficulties in follow up procedures such as device upgrading. The purpose of this study is to determine whether Aspirin or Clopidogrel are effective in the prevention of venous obstruction after implantation of cardiac pacemaker or defibrillator. 