An apparatus for use at a native valve of a heart of a subject comprises a tubular frame (30) circumscribing a longitudinal axis to define a lumen, a valve member (62) disposed within the lumen and coupled to the tubular frame, an outer frame (40), and a pin (50). The outer frame is composed of a shape-memory alloy. The tubular frame and the pin are composed of a material that is not the shape-memory alloy. The outer frame comprises a flange (42), defines an eyelet (44), and is disposed radially outward from the tubular frame. The pin defines a shaft (52) and a head (54), and couples the outer frame to the tubular frame. The head is disposed against the outer frame, radially outward from the eyelet, the shaft extends from the head through the eyelet to the tubular frame, and the shaft is welded to the tubular frame.