Relating to transcatheter stent-valves

Some embodiments of the present disclosure provide a stent-valve for transcatheter implantation to replace a cardiac valve. In some embodiments, the stent valve being compressible to a compressed state for delivery, and expandable to an operative state for implantation. In some embodiments, the stent-valve comprises a stent, a plurality of leaflets for defining a prosthetic valve, an inner skirt, an outer skirt, and a paravalve seal for sealing against surrounding tissue. In some embodiments, the paravalve seal comprising material that swells in response to contact with blood or components thereof.