An extracorporeal blood circuit, comprising: an expansion chamber having a first port for inlet of blood and a second port for outlet of blood; a first blood transport line having a first tract connected to the first port and a second tract connected to the second port; a filter arranged internally of the expansion chamber, the filter comprising a tubular filtering wall configured to retain solid small bodies in a blood flow which flows from the first port to the second port; the tubular filtering wall being provided with a plurality of lateral openings; the tubular filtering wall having a longitudinal axis (x-x); at least a part of the longitudinal axis of the tubular filtering wall extending vertically or obliquely, with reference to a use configuration of the expansion chamber; the tubular filtering wall having an open lower end communicating with the second port; the tubular filtering wall having an upper end which extends on a lie plane that is perpendicular to said longitudinal axis; the filter comprising a top head which is inferiorly delimited by the upper end of the tubular filtering wall; characterized in that the top head is provided with upper openings arranged at a lower height with respect to the first blood inlet port; wherein the upper openings form a passage for non-dissolved gas, which passage is conformed and/or arranged asymmetrically with respect to said longitudinal axis (x-x). an expansion chamber having a first port for inlet of blood and a second port for outlet of blood; a first blood transport line having a first tract connected to the first port and a second tract connected to the second port; a filter arranged internally of the expansion chamber, the filter comprising a tubular filtering wall configured to retain solid small bodies in a blood flow which flows from the first port to the second port; the tubular filtering wall being provided with a plurality of lateral openings; the tubular filtering wall having a longitudinal axis (x-x); at least a part of the longitudinal axis of the tubular filtering wall extending vertically or obliquely, with reference to a use configuration of the expansion chamber; the tubular filtering wall having an open lower end communicating with the second port; the tubular filtering wall having an upper end which extends on a lie plane that is perpendicular to said longitudinal axis; the filter comprising a top head which is inferiorly delimited by the upper end of the tubular filtering wall; characterized in that the top head is provided with upper openings arranged at a lower height with respect to the first blood inlet port; wherein the upper openings form a passage for non-dissolved gas, which passage is conformed and/or arranged asymmetrically with respect to said longitudinal axis (x-x). a filter arranged internally of the expansion chamber, the filter comprising a tubular filtering wall configured to retain solid small bodies in a blood flow which flows from the first port to the second port; the tubular filtering wall being provided with a plurality of lateral openings; the tubular filtering wall having a longitudinal axis (x-x); at least a part of the longitudinal axis of the tubular filtering wall extending vertically or obliquely, with reference to a use configuration of the expansion chamber; the tubular filtering wall having an open lower end communicating with the second port; the tubular filtering wall having an upper end which extends on a lie plane that is perpendicular to said longitudinal axis; the filter comprising a top head which is inferiorly delimited by the upper end of the tubular filtering wall; characterized in that the top head is provided with upper openings arranged at a lower height with respect to the first blood inlet port; wherein the upper openings form a passage for non-dissolved gas, which passage is conformed and/or arranged asymmetrically with respect to said longitudinal axis (x-x).