The invention relates to an insertion device that for the first time allows gaining access to the left ventricle of the heart, via the tissue forming the wall of the right ventricle and via the ventricular septum. The insertion unit comprises a tubular shaft (5) with a lumen (8) extending there through, said shaft comprising distal, proximal and central sections, whereby the distal and proximal sections are disc-shaped extended thus forming each a double disc (1), (2) resp. (3) (4) and whereby the central section (50) links the distally placed double disc (1), (2) with the proximally placed double disc (3), (4), and whereby pressure valve (6) resp. (7) are fixed inside the shaft preferably on its distal and proximal end. The invention also relates to devices using said insertion unit.