to get access to the venous system having reached access to the venous system a long guiding wire not shown of metal is advanced through the introduction sheet and via the venous system to the coronary sinus 5 this guiding wire is provided with x ray distance markers so that the position of the guiding wire in the coronary sinus 5 may be monitored the elongate body 8 is locked onto the stabilizing instrument 12 as shown in fig5 and introduced into the long cover sheet 11 of synthetic material this aggregate is then pushed through the introduction sheet and the venous system to the coronary sinus 5 riding on the guiding wire after exact positioning of the elongate body 8 in the coronary sinus 5 as illustrated in fig8 where the mitral valve 19 is shown having a central gap 20 the cover sheet 11 is retracted exposing the elongate body 8 within the coronary sinus 5 this manoeuvre allows the hooks 10 on the elongate body 8 to dig into the walls of the coronary sinus 5 and into the heart the elongate body 8 is still locked on to the stabilizing instrument 12 such that the hooks 10 engage the walls of the coronary sinus 5 in the stretched or extended state of the elongate body 8 a catheter 21 shown in fig6 is pushed forward.