Piston machine, comprising a housing with a chamber which has a substantially circle sector-shaped cross-section, a pivotal piston (101, 102) which is designed as a pivoting element, is arranged in the housing and comprises a first working surface (29, 30), wherein the housing and the piston (101, 102) define at least one first variable working chamber (A1, A2, A3), a drive or output which is connected to the piston (101, 102), an outlet valve (19a, 19b, 19c) which is arranged in the working chamber (A1, A2, A3) for discharging a working fluid, and an inlet valve (18a, 18b, 18c) which is arranged in the working chamber for admitting the working fluid into the working chamber (A1, A2, A3), wherein the housing has two or more housing parts (103a, 103b) which are each circle sector-shaped but are joined to one another rotated through 180 degrees and form a common cavity, wherein each housing part (103a, 103b) is associated with its own piston (101, 102) of the aforementioned kind, wherein two adjacent housing parts (103a, 103b) together with their pistons (101, 102) define at least one variable working chamber, wherein two adjacent pistons (101, 102) are arranged rotated through 180° relative to one another in their respective housing parts (103a, 103b), characterized in that the housing has a cooling opening (152, 160) in at least one housing wall (111, 112) for convectively cooling a side of one of the aforementioned pistons (101, 102) opposite the first working surface by means of a coolant, wherein the two adjacent housing parts each have a wall (111, 112) which has a circular arc-shaped cross-section and delimits the chamber, and a cooling opening (152, 160) is provided in both circular arc-shaped walls, wherein the cooling openings (152, 160) are arranged opposite one another so that the coolant can flow in and out from one side to the other side. a housing with a chamber which has a substantially circle sector-shaped cross-section, a pivotal piston (101, 102) which is designed as a pivoting element, is arranged in the housing and comprises a first working surface (29, 30), wherein the housing and the piston (101, 102) define at least one first variable working chamber (A1, A2, A3), a drive or output which is connected to the piston (101, 102), an outlet valve (19a, 19b, 19c) which is arranged in the working chamber (A1, A2, A3) for discharging a working fluid, and an inlet valve (18a, 18b, 18c) which is arranged in the working chamber for admitting the working fluid into the working chamber (A1, A2, A3), wherein the housing has two or more housing parts (103a, 103b) which are each circle sector-shaped but are joined to one another rotated through 180 degrees and form a common cavity, wherein each housing part (103a, 103b) is associated with its own piston (101, 102) of the aforementioned kind, wherein two adjacent housing parts (103a, 103b) together with their pistons (101, 102) define at least one variable working chamber, wherein two adjacent pistons (101, 102) are arranged rotated through 180° relative to one another in their respective housing parts (103a, 103b), characterized in that the housing has a cooling opening (152, 160) in at least one housing wall (111, 112) for convectively cooling a side of one of the aforementioned pistons (101, 102) opposite the first working surface by means of a coolant, wherein the two adjacent housing parts each have a wall (111, 112) which has a circular arc-shaped cross-section and delimits the chamber, and a cooling opening (152, 160) is provided in both circular arc-shaped walls, wherein the cooling openings (152, 160) are arranged opposite one another so that the coolant can flow in and out from one side to the other side.