Right cardiac thrombosis is an infrequent complication after pacemaker implant. We report a patient who received a biventricular implantable cardioverter defibrillator, with a large mobile thrombus, adherent to the left ventricular lead. This catheter was partially dislocated, with a large, mobile loop through the right atrium and right ventricle; so the lead thrombus could alternately obstruct the pulmonary valve and the tricuspid valve. We believe that this is the first case of left ventricular lead thrombosis, in which the surgical treatment included thrombectomy with conservation of the catheter that was anchored to the internal right atrial wall in order to limit its great motility, maintaining the contribution to the cardiac resynchronization.