Apparatus (120) is provided comprising: a longitudinal guide member (220) (a) comprising a blunt distal end (160) having an outer surface (164) at least part of which is transparent, (b) configured to be advanced distally toward a heart of a subject, and (c) shaped to define an at least partially distally-facing and side-facing suction port (660) at a distal portion (662) of the longitudinal guide member (220). The apparatus is configured to facilitate drawing a portion of a pericardium of the heart through the suction port and into the longitudinal guide member. The apparatus additionally comprises a puncturing element (50) configured to puncture the portion of the pericardium while the portion of the pericardium is in the longitudinal guide member. Other applications are also described.
