The present invention relates to a stet for the positioning and anchoring of a valvular prosthesis in an implantation site in the heart of a patient. Specifically, the present invention relates to an expandable stent for an endoprosthesis used in the treatment of a narrowing of a cardiac valve and/or a cardiac valve insufficiency. So as to ensure that no longitudinal displacement of a valvular prosthesis fastened to a stent will occur relative the stent in the implanted state of the stent, even given the peristaltic motion of the heart, the stent according to the invention comprises at least one fastening portion via which the valvular prosthesis is connectable to the stent. The stent further comprises positioning arches and retaining arches, whereby at least one positioning arch is connected to at least one retaining arch via a first connecting web. The stent moreover comprises at least one auxiliary retaining arch which connects the respective arms of the at least one retaining arch connected to the at least one positioning arch.