An introducer assembly (10) includes a catheter (12) having a proximal end (14), a distal end (16) extending to a distal tip of the introducer assembly, and an outer catheter wall. The catheter (12) includes a medical device holding portion (34) proximate the distal end, a guide wire lumen (100) extending between the proximal and distal ends, and a side opening (50) extending through the outer wall to the guide wire lumen. The side opening (50) and the guide wire lumen (100) are simultaneously open and the guide wire lumen and side opening are able to receive a guide wire therethrough. The catheter (12) is flexible at least in the location of the side opening, such that a guide wire (28) fed from the distal end (16) can pass through to the proximal end (14) when the catheter is substantially straight and can pass from the distal end through the side opening (50) when the catheter is curved at the location of the side opening. The catheter (12) also includes a plurality of one stiffening mandrel lumens (104, 106) extending from the proximal end (14) and a plurality of stiffening mandrels sized to fit within the stiffening mandrel lumens and in some forms able to slide therewithin and in other forms enclosed within the stiffening mandrel lumens. The mandrels have different lengths disposed along the length of the catheter and can be of substantially uniform diameter.
