Hydrodynamic machine, in particular retarder, having an external working medium circuit, comprising 1.1 a vaned primary wheel and a vaned secondary wheel, which form a toroidal working chamber with each other, which can be filled with working medium from the external working medium circuit, which medium is led back again into the external working medium circuit, 1.2 an annular channel arranged outside the working chamber, which is connected to the working chamber so as to conduct working medium via outlet bores in the primary wheel or secondary wheel and is connected to the external working medium circuit so as to conduct flow, in order to collect working medium emerging from the working chamber through the outlet bores and to feed the same to the external working medium circuit; characterized by the following features: 1.3 having at least one tapping opening, which is arranged on or outside the working chamber and is connected to the working chamber of the hydrodynamic machine so as to conduct flow, and at least one filling channel, which opens within the hydrodynamic machine in a region of relatively low working medium pressure and is connected to the working chamber so as to conduct flow; wherein 1.4 the at least one tapping opening and the filling channel are connected to each other so as to conduct working medium by means of a return line outside the external working medium circuit, in such a way that working medium from the at least one tapping opening flows into the filling channel and from there into the working chamber again, so that a working medium circuit is established outside the external working medium circuit. 1.1 a vaned primary wheel and a vaned secondary wheel, which form a toroidal working chamber with each other, which can be filled with working medium from the external working medium circuit, which medium is led back again into the external working medium circuit, 1.2 an annular channel arranged outside the working chamber, which is connected to the working chamber so as to conduct working medium via outlet bores in the primary wheel or secondary wheel and is connected to the external working medium circuit so as to conduct flow, in order to collect working medium emerging from the working chamber through the outlet bores and to feed the same to the external working medium circuit; characterized by the following features: 1.3 having at least one tapping opening, which is arranged on or outside the working chamber and is connected to the working chamber of the hydrodynamic machine so as to conduct flow, and at least one filling channel, which opens within the hydrodynamic machine in a region of relatively low working medium pressure and is connected to the working chamber so as to conduct flow; wherein 1.4 the at least one tapping opening and the filling channel are connected to each other so as to conduct working medium by means of a return line outside the external working medium circuit, in such a way that working medium from the at least one tapping opening flows into the filling channel and from there into the working chamber again, so that a working medium circuit is established outside the external working medium circuit.