The invention relates to a method and a device for heating an end section of a plastic pipe (1) to prepare for the formation of a sleeve on the plastic pipe, such that the end section can be heated to the deformation temperature of the plastic pipe or even higher by heating on the exterior by means of external heating jaws (2, 3) and on the interior by means of a heating mandrel (4) that can be inserted from the end into the plastic pipe (1). According to the invention, the end section is heated by means of a heating mandrel (4) with at least one first length section (6) and one second length section (5), such that the diameter along the first forward length section (6) is smaller than the internal diameter of the end section of the pipe, and the diameter of the heating mandrel (4) is increased over the second length section (5), which follows the first length section (6) toward the end of the heating mandrel (4), such that the end of the second length section (5) comes in contact with the interior of the end section of the pipe on heating the end section of the pipe, so that the end of the end section of the pipe to be heated is in contact with both the external heating jaws (2, 3) and the heating mandrel (4) when the pipe is heated.