The subject guide catheter extension/pre-dilatation system includes an outer delivery sheath, an inner member extending within the sheath, and a mechanism for engagement/disengagement of the inner member to/from the sheath. The inner member is configured with a tapered distal tip having a delivery micro-catheter and a pre- dilatation balloon member attached to the tapered distal tip in proximity to the micro- catheter. The outer delivery sheath and the inner member are modified for different engagement/disengagement mechanisms operation. The delivery micro-catheter provides for an improved crossability for the balloon member to the treatment site in an atraumatic, expedited and convenient fashion. During the cardiac procedure, a guidewire and a guide catheter are advanced to the vicinity of the treatment site within a blood vessel. Subsequent thereto, the inner member and outer delivery sheath, in their engaged configuration, are advanced along the guidewire inside the guide catheter towards the site of treatment. Once at the treatment site, the balloon member is inflated for pre-dilatation treatment. Subsequently, the inner member is disengaged and retracted from the outer delivery sheath, and a stent is delivered to the treatment site inside the outer delivery sheath.l'invention concerne un système d'extension/de pré-dilatation de cathéter de guidage comprenant une gaine d'administration externe, un élément interne s'étendant à l'intérieur de la gaine, et un mécanisme de mise en prise/libération de l'élément interne vers/depuis la gaine. L'élément interne est configuré avec une pointe distale effilée ayant un micro-cathéter d'administration et un élément ballonnet de pré-dilatation fixé à la pointe distale effilée à proximité du micro-cathéter. La gaine d'administration externe et l'élément interne sont modifiés pour différents mécanismes de mise en prise/libération. Le micro-cathéter d'administration assure une meilleure aptitude au passage de l'élément ballonnet
