The invention relates to a medical device, in particular a blood cassette (200), comprising a device body (201), at least one fluid-holding chamber (1) for holding at least one first medical fluid (5), in particular blood, and at least one hydrophobic filter device (100) having a filter surface, through which at least one second, gaseous fluid (19), in particular air, can be fed to the fluid-holding chamber (1), wherein the filter device (100) has at least one filter membrane (9)； wherein the filter membrane (9) has a back side (9a) and a front side (9b)； wherein the filter membrane (9) is welded by means of the back side (9a) thereof to the fluid-holding chamber (1), to of a wall thereof, or to another section of the cassette body (201) along a weld section (203)； wherein the filter device (100) has a front supporting structure (27) on the front side (9b), which front supporting structure is arranged to support the filter membrane (9)； wherein the front supporting structure (27) is arranged to be in contact with the weld seam section (203) by means of a first contact section (27a) of the front supporting structure (27).
