A liquid heating bag 50 is proposed, in particular, a blood heating bag, with a flow volume 1 that is formed from at least two flexible plastic foils connected to each other by welding at four delimiting edges 3,4,5,6, has a flat, substantially trapezoidal basic shape that is limited by the delimiting edges 3,4,5,6, and an inlet line opening 10 and an outlet line opening 11 for a liquid to be heated that are disposed at an upper delimiting edge 3 of the delimiting edges 3,4,5,6 to be disposed at the top during liquid heating, wherein the upper delimiting edge 3 extends sufficiently obliquely with respect to its adjacent delimiting edges 4,6 that a gas reception volume 8 is formed in the region of an acute angle of the flow volume 1 subtended between the upper delimiting edge 3 and a delimiting edge 6 adjacent thereto, and a liquid flow guiding seam 13 that is formed by connecting the plastic foils in the region of the flow volume 1 and divides the upper delimiting edge 3 into a lower inlet line opening region and an upper outlet line opening region on the gas reception volume side. A degassing opening 23 is disposed at the upper delimiting edge 3 in the region of the gas reception volume 8 between the outlet line opening 11 and the delimiting edge 6 adjacent to the outlet line opening region.