Devices, systems and methods for reducing patent discomfort during defibrillation by synchronizing defibrillation pulse delivery with a patient breathing cycle are described. Embodiments provide for a defibrillator having at least one electrode lead with one or more electrodes, a controller for determining whether fibrillation exists, a voltage generator for producing and discharging one or more electrical pulses to the electrode lead system and at least one breathing sensor for collecting and transmitting information relating to the breathing cycle of the patient to the controller. The controller may process the information from the breathing sensor, determine when one or more phases or instants of the breathing cycle are occurring and emit a command signal to the voltage generator to discharge defibrillation pulses to the electrode lead system in synchronization with the one or more phases or instants of the breathing cycle.