The invention relates to a fin for a heat exchanger, comprising a fin element which extends in the flow direction of a first fluid and has a wall face around which the first fluid flows on both sides, wherein at least one flap is provided in the wall face, which flap forms a cutout, through which the first fluid can flow, in the wall face, wherein a first edge of the flap for forming the cutout is arranged spaced apart from the wall face, wherein the flap has a tab face which is inclined with respect to the wall face and terminates at the first edge, wherein the tab face is connected to the wall face via at least one side wall, extending with a curved profile, of the flap, which side wall, starting at the first edge, has a height which decreases in a way which corresponds to the inclination of the tab face.