Electrical machine comprising - a first active part and - a second active part, wherein - both the first active part and the second active part have a plurality of laminated sub-cores, - each of the laminated sub-cores has a plurality of individual laminations, each comprising an axial width (b), - the laminated sub-cores are mutually spaced in an axial direction (a) such that a respective radial cooling slot (7, 8', 8") is formed between two adjacent laminated sub-cores, - the radial cooling slots in the first active part are offset in the axial direction (a) in relation to one another in comparison to the radial cooling slots (8', 8") in the second active part, and - the second active part comprises a cooling channel which extends in an axial direction (a) and which leads into the respective radial cooling slots (8', 8") in the second active part, wherein a coolant flow can be introduced into the cooling channel at respective border areas of the second active part, wherein the coolant flow which flows through the cooling channel is distributed over the respective radial cooling slots (8', 8'') in the second active part and from there arrives in the radial cooling slots of the first active part by way of an air gap between the first active part and the second active part, characterised in that - the sum of the axial widths (b) of all individual laminations in the first active part corresponds to the sum of the axial widths (b) of all individual laminations in the second active part, - the radial cooling slots (8', 8") in the second active part are divided into first cooling slots and second cooling slots, wherein the first cooling slots have a first axial length and the second cooling slots (8") have a greater second axial length in comparison to the first axial length, - the cooling slots (8', 8") in the second active part are arranged such that the second cooling slots (8', 8") are essentially arranged in a middle region of the second active part, wherein the middle region corresponds to a hot area of the electrical machine, and - the radial cooling slots (8', 8") in the second active part are essentially arranged symmetrically in order to achieve uniform cooling of the second active part. - a first active part and - a second active part, wherein - both the first active part and the second active part have a plurality of laminated sub-cores, - each of the laminated sub-cores has a plurality of individual laminations, each comprising an axial width (b), - the laminated sub-cores are mutually spaced in an axial direction (a) such that a respective radial cooling slot (7, 8', 8") is formed between two adjacent laminated sub-cores, - the radial cooling slots in the first active part are offset in the axial direction (a) in relation to one another in comparison to the radial cooling slots (8', 8") in the second active part, and - the second active part comprises a cooling channel which extends in an axial direction (a) and which leads into the respective radial cooling slots (8', 8") in the second active part, wherein a coolant flow can be introduced into the cooling channel at respective border areas of the second active part, wherein the coolant flow which flows through the cooling channel is distributed over the respective radial cooling slots (8', 8'') in the second active part and from there arrives in the radial cooling slots of the first active part by way of an air gap between the first active part and the second active part, - the sum of the axial widths (b) of all individual laminations in the first active part corresponds to the sum of the axial widths (b) of all individual laminations in the second active part, - the radial cooling slots (8', 8") in the second active part are divided into first cooling slots and second cooling slots, wherein the first cooling slots have a first axial length and the second cooling slots (8") have a greater second axial length in comparison to the first axial length, - the cooling slots (8', 8") in the second active part are arranged such that the second cooling slots (8', 8") are essentially arranged in a middle region of the second active part, wherein the middle region corresponds to a hot area of the electrical machine, and - the radial cooling slots (8', 8") in the second active part are essentially arranged symmetrically in order to achieve uniform cooling of the second active part.