Apparatus (40) for compressing a transcatheter cardiac stent-valve (10) comprises: a hollow channel (42) having an interior surface (50) shaped for progressively compressing the stent-valve in response to longitudinal advancement of the stent-valve within the channel; a driver (46) threadedly engaged on the exterior of the channel for generating a longitudinal driving force in response to rotation; a mover (44) having limbs (56) that project through slots (58) in the channel wall to transmit the driving force to the stent-valve within the channel; and a channel extension (48) removably attachable at the exit (54) to provide a generally cylindrical containment bore (66).