A resuscitation system for use in resuscitation of cardiac arrest victims includes an ECG monitor programmed to monitor an organized, non-shockable rhythm of an electrocardiogram (ECG) signal from a patient undergoing lifesaving cardiac care； a processor programmed to identify a time during an electrocardiographic cycle of the ECG signal during which a vulnerable period for risk of fibrillation induction of the ECG will occur； and control circuitry for generating signals to cause a parameter descriptive of chest compressions to be modified so as to minimize risk of induction of fibrillation during the vulnerable period.
