Assemblies and delivery apparatus for delivering a medical device into a patient's vasculature are disclosed. In some examples, an assembly includes a delivery apparatus and a radially compressible and expandable prosthetic heart valve. The delivery apparatus includes a handle, a first shaft and a second shaft extending from the handle, and a locking mechanism to prevent axial movement of the second shaft relative to first shaft. The second shaft extends coaxially through the first shaft and includes, at a distal end portion thereof, a balloon, one or more radiopaque markers, and the prosthetic valve radially compressed over the balloon. A flared end piece extending from the first shaft covers a proximal portion of the balloon during advancing of the delivery apparatus through a patient's vasculature. The first shaft is retractable relative to the second shaft to expose the balloon from the flared end piece.