Abstract: In a blood pump for assisting cardiac output, including a housing with a housing inlet and a housing outlet, wherein the housing forms a first pump housing and a second pump housing, a rotor which is mounted in the housing and is rotatable about an axis, wherein the rotor comprises a first pump stage with a first impeller arranged in the first pump housing and a second pump stage with a second impeller arranged in the second pump housing, wherein the first and the second pump stages are each formed as radial or diagonal pumps and through which the blood to be pumped from the housing inlet to the housing outlet can flow in succession, the first pump housing and the second pump housing are connected via a channel which runs radially outside a middle section of the housing arranged between the first and the second pump housing.