A defribrillator comprises first and second electrodes (A, B) for application to a patient, a voltage source (60), and an output circuit for connecting the voltage source across the electrodes upon the occurrence of a control signal (64). The output circuit includes a first current path connecting one side of the voltage source to the first electrode (A) and a second current path connecting the other side of the voltage source to the second electrode (B). Each of the current paths contains at least one solid state switching device USD1 (bo) or IGBT1. The switching device(s) USD1 (bo) in at least one of the current paths has no external control and characteristics similar to a Shockley diode.