A medical instrument for engaging tissue includes a flexible shaft, a tissue piercing coil at a distal portion of the shaft, and a tissue stabilizer positioned over the shaft and biased in a distal direction such that as the tissue piercing coil enters tissue, the tissue stabilizer is urged against a surface of the tissue. A medical instrument for reconfiguring tissue includes a flexible shaft defining a lumen housing actuating controls, and a distal actuating assembly with a sealing portion configured to substantially seal the shaft lumen from contact with bodily fluids. A cartridge assembly includes first and second members configured for releasable attachment to a medical instrument, and a holder configured to receive the first and second members and to be released from the first and second members upon action of the first and second members attaching to the medical instrument.