The invention relates to a non-return valve, in particular for a refrigeration or heat circuit, which valve can be inserted into a connection opening (26, 27, 28, 29) of a connection device (21) or of a pipe (39) and comprises: —a one-part or multi-part housing (42) which comprises at least one main housing (44), a feed opening (48) being provided on the inlet side and a discharge opening (51) being provided on the outlet side of the main housing (44), the feed opening and the discharge opening being interconnected by a flow channel (49); —a guide element (53) which is provided on the main housing (44) and by means of which a valve closing element (61) is guided slidably relative to the main housing (44), the valve closing element (61) being arranged in a starting position (42) by means of an energy accumulator (71) and the valve closing element (61) being slidable toward the discharge opening (51) against an actuating force of the energy accumulator (71) in order to be transferred into a working position (63), and the energy accumulator (71) being provided between the valve closing element (75) and the main housing (44), the guide element (53) of the main housing (44) having at least one through-hole (57) and at least one guide rod (59) being guided in said at least one through-hole (57), which rod at least extends from the valve closing element (61) through the at least one through-hole (57) and is secured against release from the through-hole (57), or the guide element (53) being designed as a sleeve (54) having a bottom (55), which is associated with the discharge opening (51), and the valve closing element (61) having a guide portion (66) which acts on the sleeve (54).