A resuscitation system for use by a rescuer for resuscitating a patient having a ventricular arrhythmia, comprising circuitry and processing configured for detection of chest compression/phase timing information indicative of the start of the decompression phase, circuitry and processing configured for delivery of electromagnetic therapy for the termination of ventricular arrhythmias, wherein the circuitry and processing for the delivery of electromagnetic therapy utilizes the chest compression phase timing information to initiate delivery of the electromagnetic therapy within 300 milliseconds of the start of the decompression phase.