Guide extension catheters and related methods are disclosed. A guide extension catheter can comprise an elongate tube member, a push member, and a concave track. The elongate tube member can define a lumen and three distinct portions of different diameter. A distal portion can define a first diameter, a proximal portion can define a second diameter which is larger than the first diameter but smaller than a lumen of a guide catheter with which the guide extension catheter is used, and a tapered portion, positioned between the distal portion and the proximal portion, can have a variable diameter. The push member can be eccentrically coupled relative to the tube member and extends proximally therefrom for slidably positioning the tube member within and partially beyond a distal end of the guide catheter. The concave track forms a transition between the tube member and the push member, and defines a partially cylindrical opening leading into the tube member.
