Transluminal delivery system

Apparatus for use at a heart of a subject, the apparatus comprising:

• a delivery tool dimensioned for percutaneous delivery to the heart, the delivery tool having a distal portion that defines a central longitudinal axis at the distal portion and comprises:
• a shaft;
• and
• a proximal capsule and a distal capsule, each of the capsules:
• having a respective open end, the open end of the proximal capsule facing the open end of the distal capsule, and
• coupled to the shaft in a manner that allows axial movement of the capsule with respect to the shaft, along the central longitudinal axis at the distal portion;
• and
• a prosthetic heart valve comprising:
• a tubular portion that defines a lumen;
• and
• a plurality of prosthetic leaflets disposed within the lumen,
• wherein:
• the prosthetic heart valve is restrainable in a compressed state by the delivery tool, such that a downstream end of the tubular portion is disposed within the distal capsule, and
• the distal capsule is shaped so as to define an opening for visualizing ensheathing of at least a portion of the downstream end of the tubular portion within the distal capsule.