A patient with a ten-year permanent implantation of a pacemaker was admitted on account of a clinically serious syndrome of the vena cava superior. The cause of the syndrome was an angiographically confirmed extensive thrombosis and after its dissolution a fibrous septum in the area of the orifice of the vena cava superior into the right atrium. The septum caused by a fibrous strip at the orifice of the vena cava superior into the right atrium was removed by surgical operation during thoracotomy by dilatation of the original opening in the fibrous septum by a Broca dilator and digitally. The authors recommend, based on their own experience and data in the literature, to use fibrinolytic therapy in clinically severe thrombosis in the area of the vena cava superior or the right atrium caused by an electrode--during temporary or permanent pacing--or by a catheter used for parenteral nutrition.