A medical delivery system for delivering an implantable medical device including an engagement region, comprising: a delivery device for delivering the implantable medical device comprising: (a) a first delivery mechanism including (i) a first elongate member having a first elongate member lumen and (ii) an expandable member having an expandable member lumen and a first lateral width when in a relaxed state, the expandable member being positioned distal to the first elongate member; and (b) a second delivery mechanism including (i) a second elongate member and (ii) an increased diameter member having a proximal facing surface, the increased diameter member being positioned distal to and mechanically coupled to the first elongate member; wherein the second elongate member is at least partially positioned within the first elongate member lumen and the expandable member lumen, wherein the second elongate member is axially moveable relative to the first elongate member lumen and the expandable member lumen, and wherein the increased diameter member is positioned distal to the second elongate member such that when the second elongate member is pulled proximally relative to the first elongate member the proximal facing surface of the increased diameter member engages the expandable member and expands the expandable member to an expanded state having a second lateral width that is greater than the first lateral width; characterized by the implantable medical device including the engagement region, wherein the expandable member is insertable into the engagement region, wherein the expandable member is slidable within the engagement region when in the relaxed state, and wherein the expandable member is configured to laterally expand to engage with the engagement region when in the expanded state. a delivery device for delivering the implantable medical device comprising: (a) a first delivery mechanism including (i) a first elongate member having a first elongate member lumen and (ii) an expandable member having an expandable member lumen and a first lateral width when in a relaxed state, the expandable member being positioned distal to the first elongate member; and (b) a second delivery mechanism including (i) a second elongate member and (ii) an increased diameter member having a proximal facing surface, the increased diameter member being positioned distal to and mechanically coupled to the first elongate member; wherein the second elongate member is at least partially positioned within the first elongate member lumen and the expandable member lumen, wherein the second elongate member is axially moveable relative to the first elongate member lumen and the expandable member lumen, and wherein the increased diameter member is positioned distal to the second elongate member such that when the second elongate member is pulled proximally relative to the first elongate member the proximal facing surface of the increased diameter member engages the expandable member and expands the expandable member to an expanded state having a second lateral width that is greater than the first lateral width; characterized by (a) a first delivery mechanism including (i) a first elongate member having a first elongate member lumen and (ii) an expandable member having an expandable member lumen and a first lateral width when in a relaxed state, the expandable member being positioned distal to the first elongate member; and (b) a second delivery mechanism including (i) a second elongate member and (ii) an increased diameter member having a proximal facing surface, the increased diameter member being positioned distal to and mechanically coupled to the first elongate member; the implantable medical device including the engagement region, wherein the expandable member is insertable into the engagement region, wherein the expandable member is slidable within the engagement region when in the relaxed state, and wherein the expandable member is configured to laterally expand to engage with the engagement region when in the expanded state.