There is provided an energy delivery device comprising a storage device, a discharge circuit and a disarm circuit. The discharge circuit comprises a switch electrically connected to the storage device, and is selectively operable to deliver energy from the storage device to a load, e.g., a patient needing defibrillation, preferably in a multiphasic waveform. The disarm circuit comprises the switch. Preferably, the discharge circuit comprises an H-bridge circuit. There are also provided delivery devices: which comprise a shoot-through elimination circuit; which include housing elements which, when assembled, cause electrical connection between respective components; which include a housing having a small volume and an energy storage device having a large capacitance; which comprise a shunt circuit which, when activated, prevents switching of a switch. There are also provided methods of assembly and disassembly of an energy delivery unit and methods of delivering energy to a load.