Devices and methods useful for sealing bodily openings

A system for use in closing an opening in a vessel wall, comprising:

• a sheath having an insertion portion with a distal end for insertion into the vessel and a proximal head portion, said head portion having a proximal opening of a first diameter and a second opening into said insertion portion having a second diameter smaller than the first diameter;
• a delivery tube having a proximal end, a distal end, and a longitudinal lumen between said ends, the delivery tube being at least partially within said sheath;
• and
• a seal within said delivery tube, wherein a filament is fixed to said seal, the seal member being dome-shaped in a relaxed configuration and deformable under tension applied through said filament to at least partially flatten and urge a peripheral region having a rim against an interior surface of the vessel wall, and further including a mass of compressible material connected to said filament proximal of said seal, and a locking member proximal of said mass of compressible material, with said filament extending through said locking member and the locking member having a central opening and slidable along said filament so as to compress said compressible material against an external surface of the vessel and separate the locking member from the external surface of the vessel when the system is in a locked condition.