A device (10) for tissue coagulation, in particular for fusion, encompasses an electric source (18), which is connected or which can be connected to electrodes (12, 13) for influencing biological tissue (11) with current. A control unit (22) controls the source (18) during phases I and II of the tissue fusion. These phases I and II correspond to operating phases I, II and III of the device (10). During operating phase I, a monitoring unit (23) determines the energy E1, which is applied into the tissue (11). In the subsequent operating phases II and III, the control unit (22) controls the source (18) by means of the determined energy E1. Such a device turns out to be particularly reliable and to be robust in use.