Apparatus and methods are described, including apparatus comprising a longitudinal guide member comprising a blunt distal end having an outer surface at least part of which is transparent. The guide member is advanced distally toward a heart of a subject. A sheath is shaped and sized to surround the guide member and shaped to define an at least partially distally-facing suction port at a distal end of the sheath. A portion of a pericardium of the heart is drawn through the suction port and into the sheath, when the suction port is distal to the guide member. A puncturing element punctures the portion of the pericardium while the portion of the pericardium is in the sheath, and a puncturing-element-restraining element inhibits passage of a distal tip of the puncturing element out of the distal end of the sheath. Other applications are also described.
