1. A method of operation in an implantable cardiac stimulus device (ICSD) comprising a housing that contains a battery power source and operational circuitry that operates by analyzing cardiac signals from implanted electrode(s) in order to determine whether a treatable arrhythmia is detected, the method comprising: the ICSD making an initial determination that a treatable condition is occurring; the ICSD preparing to deliver therapy in response to the initial determination and, while preparing to deliver therapy, observing whether indications of benign cardiac rhythm are detected; when the ICSD is prepared to deliver therapy, applying Confirmation criteria to confirm the treatable condition is ongoing; and if the Confirmation criteria are met, delivering therapy from the ICSD; wherein the method comprises the ICSD changing the Confirmation criteria in response to identification of one or more indications of a benign cardiac rhythm while the ICSD is preparing to deliver therapy.